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Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions - 1999
Authors: Larry R. Teuber, Larry K. Gibbs, and Kenneth L. Taggard Affiliation & Location: Agronomy and Range Science, University of California, Davis, CA 95616-8515 Progress in Breeding Alfalfa for Resistance to the Silverleaf Whitefly The silverleaf whitefly (Bemisia argentifolii Bellows and Perring) has been recognized as a serious pest in Low Desert alfalfa production since 1991. Annual losses are estimated to exceed $26 Million in Imperial County, California alone. In October 1992, we identified 73 individual plants exhibiting little if any stickiness and fewer whitefly nymphs than commercially available cultivars. During the next two production seasons evaluation procedures, estimates of genetic variance, and a plant breeding protocol were developed. Using the estimates of genetic variance we predicted that three to five cycles of selection would be necessary to develop economic resistance to the silverleaf whitefly. Selection is based on an index using subjective ratings for both stickiness and number on immature whiteflies on the foliage (both are scored on a 1=clean to 5=severe damage scale). The breeding protocol includes among-and-within half-sib family selection and a winter seed increase nursery in South America (Chile). Following four cycles of selection we have developed populations characterized by significantly reduced presence of whitefly nymphs and stickiness on the foliage. These characteristics have been incorporated into a genetic background that is adapted to hay and forage production in the Low Desert. Experimental cultivars are now in the seed increase process and we expect to have commercial seed of a cultivar available to growers in January 2001. Studies have been initiated to determine the mechanism of resistance. Investigator's Name(s): J. L. Bi, G. R. Ballmer, & N. C. Toscano.
Affiliation & Location: Department of Entomology, University of California, Riverside, CA92521.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1998
Effect of Nitrogen Fertility on Cotton-Whitefly Interactions
The impact of nitrogen fertility on silverleaf whitefly (Bemisia argentifolii Bellows & Perring) population dynamics and honeydew production, and the related biochemical and physiological mechanisms involved, were investigated in cotton (Gossypium hirsutum L., c.v. Acala) in California. Five nitrogen levels were evaluated using urea in a randomized complete block design with five replicates. Treatments consisted of soil applications of 0, 100, 150, and 200 lbs nitrogen per acre, and a soil application of 100 lbs nitrogen together with a foliar application of 10 gal of low-biuret urea per acre. In comparison with the control treatment (0 lbs nitrogen per acre), applied nitrogen to cotton plants increased densities of silverleaf whiteflies per fifth node leaf throughout the season. Within the nitrogen treatments, the higher rates of application (150 and 200 lbs nitrogen per acre) resulted in higher densities of whiteflies. Higher nitrogen treatments also resulted in higher densities of honeydew drops produced by the whiteflies. The impact of nitrogen fertility on whitefly densities and honeydew drop densities was more apparent in late season. Also, the nitrogen treatments generally enhanced cotton foliar photosynthetic rates and altered concentrations of several soluble carbohydrates such as glucose, fructose, and sucrose in cotton petiole. These results suggest that nitrogen fertility is an important determining factor controlling whitefly population dynamics and honeydew production. The precise biochemical and physiological mechanisms involved are currently being evaluated and will be discussed.
Investigator's Name(s): Nathalie Boissot & Claudie Pavis.
Affiliation & Location: INRA, Unité de Recherches en Productions Végétales, F-97170 Petit-Bourg, Guadeloupe (F.W.I.).
Research & Implementation Area: Section E: Host-Plants Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1998
Resistance Against Bemisia tabaci B Biotype in Melon
In Guadeloupe and Martinique (French West Indies), Bemisia tabaci outbreaks have occurred since 1990, especially on cucurbits. The whitefly was described as Bemisia tabaci B biotype (Sauvion et al., submitted). We started to study the host plant resistance in Cucumis melo in 1997.
In 1997/98, 68 genotypes (from the germplasm collection of INRA-Avignon, France) were tested under natural infestation (66 Cucumis melo, 1 Benicase cerifera, 1 metuliferus). Sixteen plants per genotype (4 plants x 4 plots were observed: 1) 2 and 4 weeks after planting (WAP), the adults were counted under 2 leaves/plant. 2) 4,5,6 and 7 WAP, the eggs were counted under 2.22 cm2 leaf discs/plant. 3) 6,7,8, and 9 WAP, the larvae were counted under 2.2 cm2 leaf discs/plant, the discs were sampled on the same leaves as for the eggs, at 4,5,6 and 7 WAP, respectively.
The adult counts allowed to estimate the importance of the natural infestation. Resistance parameters are evaluated from the egg counts (antixenosis for egg-laying) and from the relationship between the number of eggs and the number of larvae (an indicator of antibiosis). As infestation level can be variable, Vèdrantais was present in each trial. Some genotypes as OuzbËque 1, Top Mark, Iran B or B66-5 were more susceptible than Vèdrantais. Six genotypes were tested in 1997 and 1998: 90625, Kanro Makuva, PI 161375, PI 414723, Gaizabadi Phoont and HSD 200 and scored better than Vèdrantais. Among the 68 genotypes tested,, 26 were described resistant to Aphis gossypii. The variability in the scoring of those genotypes (better or worst than Vèdrantais) showed that the resistance against Bemisia tabaci B and Aphis gossypii were independent. From this screening, it appears that 10 genotypes have possibly partial resistance against Bemisia tabaci B (antixenosis and antibiosis).
The second step of the study was to develop a bioassay in order to quantify resistance to egg-laying and to larval development. This was made using synchronized mass-rearing. These preliminary tests allowed to determine the following optimal conditions for bioassaying. Adults are collected in the rearing cage during the emergence peak. Females are separated from males under binocular microscope at 10°C, after been placed 2½ minutes at 12°C. Thirty females are then allowed to lay eggs during 6 hours, on the second leaf of a 3-leaf plant. Plants are grown in climatic chamber (T=27 ± 1°C, HR=85 ± 10%). After 5 and 10 days, respectively, eggs and larvae are counted. Adult emergences are daily recorded counting empty puparial exuviae. The emergence curve follows a Gompertz distribution, where the m parameter indicates the mean larval development duration. The germplasm evaluation is now in progress, using this standardized bioassay.
Sauvion, N., C. Pavis, A. Huc, M. Rousseau, and N. et Boissot. Caractérisation de Bemisia tabaci biotype B (Hempitera: Aleyrodidae) en Guadeloupe. Ann Soc. Entomol Fr.
Investigator's Name(s): Nathalie Boissot, Denis Lafortune, Georges Ano, Claudie Pavis, & Nicolas Sauvion.
Affiliation & Location: INRA, Unit de Recherches en Productions Vegetales, F-97170 Petit-Bourg, Guadeloupe (F.W.I.).
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: January 1, 1996 - August 31, 1998
Resistance Against Geminivirus and Bemisia tabaci B in Tomato and Melon
In Guadeloupe and Martinique (French West Indies), Bemisia tabaci outbreaks have occurred since 1990, especially on Cucurbits with its concomitant geminivirus epidemics on tomato crops. The whitefly was described as Bemisia tabaci B biotype and the geminivirus as the PYMV (see Urbino et al., in this progress report).
Facing this situation, INRA developed two programs on host plant resistance:
· Tomato resistance against geminivirus: first, field screening under natural infestation allowed to identify genitors of resistance to PYMV. Eighty plants per genotype were observed in 1996/97/98 (20 plants x 4 plots). Symptoms were observed every week and rated through a 1 to 5 scale. More than 80 genotypes (families, F1 hybrids and inbred lines) were tested. Those genotypes mainly came from populations bred for resistance against TYLCV by Henri Latterot (INRA Avignon, France). The rating varied from 2 to 5, indicating that partial resistance against PYMV is present in the tested genotypes. As Ralstonia solanacearum is a major constraint in the West Indies, the second step of the program was to associate the complete resistance against R. Solanacearum (from the inbred line `Caraïbo') to the partial resistance to PYMV observed in different sources. Crosses were made and the F3 families were tested for resistance against the two pathogens in different trials. Inbred lines are under way to be obtained from the best families. · Melon resistance against Bemisia tabaci B biotype: In 1997/98, 70 genotypes (from the germplasm collection of INRA-Avignon, France) were tested under natural infestation. Sixteen plants/genotype (4 plants x 4 plots) were observed : * 2 and 4 weeks after planting (WAP), the adults were counted under 2 leaves/plant. * 4, 5, 6 and 7 WAP, the eggs were counted under 2.22 cm² leaf discs/plant. * 6, 7, 8 and 9 WAP, the larvae were counted under 2.22 cm² leaf discs/plant, the discs were sampled on the same leaves as for the eggs, at 4, 5, 6 and 7 WAP respectively.
The adults counts allowed to estimate the importance of the natural infestation. Resistance parameters were evaluated from the egg counts (antixenosis for egg-laying) and from the relationship between the number of eggs and the number of larvae (an indicator of antibiosis). From this screening, it appears that 10 genotypes have possibly partial resistance against Bemisia tabaci B (antixenosis and antibiosis). We are now developing bioassays to analyze and quantify the resistance.
Investigator's Name(s): James S. Bucknerl, Thomas P. Freeman2, C.C. Chu3, Dennis R. Nelson1, & Thomas J. Henneberry3.
Affiliation & Location: 1USDA-ARS, Biosciences Research Lab., Fargo, ND; 2Electron Microscopy Center, Plant Pathology Department, North Dakota State University, Fargo, ND; 3USDA-ARS, Western Cotton Research Lab., Phoenix, AZ.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1998
Whitefly Egg Pedicel Morphology and Penetration Characteristics
Whitefly eggs are generally elongate-oval and the basal end has a pedicel or stalk of varying length by which the female attaches the egg to a plant leaf. B. argentifolii females insert the pedicel into a slit made in the leaf by the ovipositor and secrete a glue-like substance around the pedicel. In addition to anchoring the egg to the leaf surface, the indicated function of the pedicel is to serve as a conduit for absorbing water to protect the egg from dehydration. Using established methods for leaf tissue fixation, embedment, sectioning and staining, the penetration characteristics of B. argentifolii eggs inserted into cotton leaves were observed by both light and transmission electron microscopy. Scanning electron microscopy (SEM) was used to observe and characterize oviposited eggs removed from cotton leaves and artificial membranes. The morphology of the pedicel of eggs removed from leaves and membranes was compared to the pedicel of eggs removed from the ovaries of gravid B. argentifolii females.
For cotton leaves, the pedicels B. argentifolii eggs were most often inserted into abaxial epidermal cells. We observed that the distal end of most pedicels was curved within the plant epidermal cells. A glue-like substance was observed to envelop the base of the pedicel, but not the tip region. This glue-like collar was also observed on the pedicel of eggs removed from artificial membranes. These findings imply that the female secretes the glue-like substance at the time of egg insertion.
SEM observations of eggs removed from ovaries indicate that the pedicels have two distinct morphological areas. The proximal portion of the pedicel appears as an extension of the smooth-surfaced egg chorion. The distal end of the pedicel appears to be covered with an array of tangled-like fibers. Longitudinal sections of oviposited B. argentifolii eggs show the chorion layer ending along the upper portion of the pedicel. This fibrous appearance at the distal end of the pedicel supports the suggestions and evidence for water uptake into the egg.
Investigator's Name(s): 1C. C. Chu, 1A. C. Cohen, 2E. T. Natwick, 3G. S. Simmons, & 1T. J. Henneberry.
Affiliation & Location: 1USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ, 2University of California Imperial County Cooperative Research and Extension Center, Holtville, CA, and 3USDA-APHIS PPQ WR, Brawley, CA.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1996
Silverleaf Whitefly Colonization and Leaf Morphology Relationships in Upland Cotton Cultivars
Studies were conducted at Holtville, CA in 1996 to investigate the relationships between upland, Gossypium hirsutum L., leaf morphology and whitefly population densities. There were eight United States Deltapine (DPL) cultivars: DPL 20, 50, 90, 5415, 5432, 5461, 9050, and 9057 and six Australian cotton cultivars and breeding lines, CS 50, Siokra 1-4/649, Siokra L23, Siokra V-15, 87031-126, and 89013-114. Results showed that Australia okra-leaf cultivars and lines were colonized with fewer whitefly adults, eggs and nymphs compared to Australia and United States normal-leaf cultivars. The distances from underleaf surfaces of cotton leaves to the centers of nearest minor vascular bundles was negatively correlated with whitefly adult, egg and nymphal densities on leaves for all genotypes with exception of the Australian breeding line 89013-114. Our results suggest that the okra-leaf character and the distance from underleaf surfaces to the center of nearest minor vascular bundles of cotton leaves are genetic traits that have potential for breeding whitefly resistant upland cotton cultivars.
Investigator's Name(s): 1C. C. Chu, 2T. P. Freeman, 3J. S. Buckner, 4E. T. Natwick, 3D. R. Nelson, & 1T. J. Henneberry.
Affiliation & Location: 1USDA-ARS, Western Cotton Research Lab., Phoenix, AZ, 2Electronic Microscopy Center, North Dakota State University, Fargo, ND, 3USDA-ARS Bioscience Research Laboratory, State University Station, Fargo, ND, & 4University of California Imperial County Cooperative Research and Extension Center., Holtville, CA.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1996 - 1998
Silverleaf Whitefly Oviposition on Upland Cotton Cultivars
Silverleaf Densities and Egg Distribution on Selected Upland Cotton Cultivars. Oviposition as a critical life stage of silverleaf whitefly reproduction has been used an indicator of adult behavior, host plant preferences, host plant resistance, leaf age preference, and effectiveness of insecticide treatments. It has been reported to be affected by leaf trichomes, leaf age and leaf position on the stems, leaf moisture and temperature, and nutritional condition of leaves. After landing on cotton leaves, silverleaf whitefly adult females immediately begin stylet probing activities on leaf surfaces. Eggs laying may occur before stylets penetrate into phloem tissue. Whitefly egg distributions are aggregated and in cotton, eggs are generally laid on or within ca. 30 mm of vascular bundle-associated elongated epidermal cells. We report here on silverleaf whitefly adult, nymph and egg densities on cotton leaves, an examination of the egg distribution and mechanisms of ovipositional site selections in relation to underleaf surface features of five upland cotton cultivars: Deltapine (DPL) 50, 5415 and 5432, Fibermax 832 and Siokra L23. Deltapine 5415 and 5432 had the highest and Siokra L23 the lowest numbers of eggs and nymphs. Siokra L-23 also had the lowest number of adults compared to the other four cultivars. On the average, 72% of the eggs were laid on leaf surfaces between veins and 25 % were laid on veins that were £ 4 or fewer cells wide. Few eggs were found on veins that were 5 or more cells wide. No eggs were inserted into leaf stomata.
Silverleaf Whitefly Egg Penetration in Upland Cotton Leaves. Silver leaf whitefly adults laid eggs almost exclusively on the lower surface of cotton leaves while the adults were resting or feeding. Eggs are oval shaped about 105 mm long and 60 mm in diameter. Eggs were laid randomly depending on the locations where adults were feeding or resting. Adults insert their ovipositors into lower epidermal cells, lay one egg at a time with the pedicel anchored directly into or between cells. The egg pedicel may penetrate completely through the epidermal cell into a mesophyll cell or the intercellular space between mesophyll cells. The pedicel of all eggs were surrounded by a `cement' which appeared to anchor the eggs into the leaf tissue. The composition of the `cement' is unknown.
Investigator's Name(s): 1Thomas P. Freeman, 2C. C. Chu, 3James S. Buckner, 3Dennis R. Nelson, & 2Thomas J. Henneberry.
Affiliation & Location: 1Electron Microscopy Center, Plant Pathology Department, North Dakota State University, Fargo, ND 58102; 2USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ; 3USDA-ARS Bioscience Research Laboratory, Fargo, ND.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1998
Variations in Cotton Leaf Morphology Related to Whitefly Feeding
Whiteflies (Bemisia argentifolii) are known to prefer some cotton varieties over others. There has been considerable speculation as to why this is the case. Differences in leaf morphology between varieties have frequently been considered to be a major factor. In an effort to test this hypothesis, we examined two varieties of cotton grown in Arizona during the 1998 growing season. The seasonal means of adults, eggs and nymphs on cotton leaves for the period 22 July1998 to 23 September, 1998 were: ST474 19.36 adults per leaf, 14.96 eggs per square centimeter leaf disk, 4.12 nymphs per square centimeter leaf disk compared to DPL5415 with 7.59 adults per leaf, 0.86 eggs per square centimeter leaf disk, and 0.36 nymphs per square centimeter leaf disk. The morphological-anatomical characteristics of seven leaves along the main stem of three plants of each variety were examined. Leaf 1, 3, 5, 7, 10, 15 and 20 were selected. Leaf 1 is the youngest leaf at the apex of the plant with leaves 3-20 located at successively lower nodes. The average size of leaf 1 at the time of collection was approximately 11 square centimeters. The parameters examined included; total leaf area, areole area, number of terminal vein endings per unit leaf area, number of mucilage ducts per unit leaf area, leaf thickness, distance from lower epidermis to phloem tissue, and the number of trichomes per unit leaf area.
There were differences recorded in leaf area between the two varieties but these differences were not consistent in leaves of different ages and in all replicates. Leaf 20 was always smaller in area and thinner than leaves 10 or 15.
Cotton leaf thickness and phloem depth are frequently considered to be the major morphological characteristics responsible for varietal selection by whiteflies. The measured difference in these characteristics was not very great between ST474 and DPL5415, and probably cannot be used to explain the noted preferences of one variety over the other. There were, however, very significant differences between young and old leaves in each variety which no doubt does explain why younger leaves are preferred. In leaf 1 of both varieties the phloem was located approximately 50 microns from the lower epidermis. Normal leaf expansion results in the phloem being much deeper, as great at 130 microns in leaf 15. This may be a depth too great to be reached by either adults or nymphs.
Portions of each leaf were cleared to determine the vascular pattern. It was possible using this technique to determine the average areole area as well as the number of terminal vein endings per unit leaf area. Here again there were few differences between the varieties but significant differences between leaves of different ages. The areole area was much smaller in younger leaves which means that both whitefly adults and nymphs can reach phloem tissue from almost any position on the leaf surface. This may account for the preference of young leaves over older more mature leaves on the same plant.
The number of mucilage glands per unit leaf area did not appear to differ between ST474 and DPL5415 and therefore, probably does not play a major role in variety selection by the whiteflies. The differences detected between younger and more mature leaves was related to normal leaf expansion.
The number of elongated trichomes was significantly different between the two cotton varieties and may be related to why whiteflies prefer ST474 to DPL5415.
Investigator's Name(s): Rufus Isaacs1, David N. Byrne2, & Sanjay Desai2.
Affiliation & Location: 1 Michigan State University, East Lansing, MI 48824, 2 University of Arizona, Tucson, AZ 85721.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1996
Behavioral and Developmental Effects of Trichome Defenses in Datura wrightii on Bemisia
Plant morphology can have a strong impact on whitefly population dynamics, especially in the case of leaf surface characteristics that physically prevent feeding or that cause mortality directly. In this study, three lines of a common weed species of the southwestern US, Jimson weed (Datura wrightii) were investigated for their ability to prevent colonization by Bemisia tabaci whiteflies. This weed species acts as an important non-crop reservoir for whiteflies, and different lines of D. wrightii were collected from the wild that exhibit marked variation in the form and extent of their leaf-based defenses. The three lines differed in the density of trichomes, and in the extent to which these trichomes were glandular. This variation provided a situation in which the importance of the density and glandularity of trichome defenses could be critically evaluated.
Observations of the behavior of whiteflies encountering the surfaces of young, medium and mature leaves were performed using a microscope system with data recorded onto a computer-based event recorder. These experiments demonstrated the importance of glandular hairs in preventing egg laying by trapping adult female whiteflies soon after leaf contact. In choice tests, adult whiteflies were released inside cages containing leaves of all three lines of D. wrightii. The number of insects found alive on leaves in this experiment over an 8 h observation period was significantly affected by both the density of trichomes and the presence of trichome glands. The greatest impact on whitefly survival was found on the glandular line, wherein the number of dead insects steadily increased over time. Adult whiteflies that were flying within the cages were trapped by the defenses of this line and did not escape. In addition, observations of adult eclosion from nymphs that has survived below the trichome glands, showed that these insects were instantly trapped during their movement from the site of emergence.
These data provide further strong evidence for the potential of trichome-based defenses for whitefly mitigation in agricultural systems. Selective manipulation of the weed population around crop plants may be a practical method for suppression of whitefly immigration, in contrast to the general recommendations for weed removal.
Investigator's Name(s): D. Michael Jackson, Mark W. Farnham, & Alvin M. Simmons.
Affiliation & Location: USDA-ARS, U. S. Vegetable Laboratory, Charleston, SC.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1997 - 1998
Effects of Interplanting of Collard Phenotypes on Resistance to Whiteflies
We previously reported that in small-plot experiments, glossy collard phenotypes averaged significantly fewer whitefly adults and nymphs than did standard, nonglossy phenotypes. Glossy phenotypes have reduced concentrations of leaf waxes, which causes their glossy or shiny appearance. One collard cultivar of particular interest is `Green Glaze', which segregates into glossy (resistant) and nonglossy (susceptible) phenotypes. We also previously reported that an unrelated, nonglossy cultivar, `Blue Max', had significantly fewer whitefly adults, nymphs, and eggs than other nonglossy cultivars. However, `Blue Max' is not as resistant as any glossy collard, and its mechanism of resistance is not known.
In 1997 and 1998, we evaluated the effects of an interplanting pattern of resistant and susceptible collard on whitefly infestations and on the occurrence of natural parasitoid species. The two phenotypes of `Greenglaze' (glossy and nonglossy) were evaluated for infestations of Bemisia argentifolii in mixed and solid plantings. Over a twoyear period, there were no differences in the abundance of whiteflies on the glossy phenotype when it was planted in solid 20plant plots or when it was alternated (every other plant) with the nonglossy (susceptible) phenotype. However, for some of the data sets, the numbers of whiteflies on the nonglossy phenotype in mixed plots were reduced. Overall, `Greenglaze'Nonglossy/Solid Planting had 52% of the whitefly adults counted, `Greenglaze'Nonglossy/Mixed Planting had 38%, `Greenglaze'Glossy/Solid Planting had 4%, and `Greenglaze'Glossy/Mixed Planting had 6%. In 1998, yellow sticky card traps were placed in the field during the peak whitefly period, and native parasitoids were monitored. Significantly higher numbers of whitefly parasitoids were collected from sticky cards in the solid plantings of `Greenglaze'Nonglossy, and very few parasitoids were found in the solid plantings of `Greenglaze'Glossy. Counts of parasitoids on sticky cards in the mixed plots were intermediate.
A similarly designed experiment was setup in 1998 with plants of the resistant `Blue Max' and the susceptible `Morris Heading' collard cultivars. Again, there was no difference in the resistance of `Blue Max' in either planting scheme, but late in the season when whitefly populations were very large, the number of whiteflies on the susceptible cultivar was reduced in the mixed plots. Overall, `Morris Heading'/Solid Planting had 46% of the whitefly adults, `Morris Heading'/Mixed Planting had 34%, `Blue Max'/Solid Planting had 10%, and `Blue Max'/Mixed Planting had 10%. These data show that planting pattern is relatively unimportant in the deployment of these sources of host plant resistance.
Investigator's Name(s): E. T. Natwick1, C. G. Cook2, R. L. Gilbertson3, & Young-Su Seo3.
Affiliation & Location: 1University of California Coop. Ext., Holtville, CA, 2United Agri Products, Santa Rosa, TX, and 3University of California, Davis, CA.
Research & Implementation Area: Section E: Host Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: March - December 1998
Cotton Leaf Crumple Geminivirus Disease Resistance In Upland Cotton
Nine upland cotton, Gossypium hirsutum L., cultivars or experimental breeding-lines were evaluated in the field for resistance to the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, transmitted cotton leaf crumple disease caused by cotton leaf crumple geminivirus (CLCV) in Imperial Valley, CA in 1998. The cultivars were Texas 121 and Stoneville 474 and the breeding-lines with Cedix parentage were C118-2-93, C952103, C95383, C953109, C95483, C95271, and C95387. Disease symptom ratings for CLCV (1= no symptoms, 2= mild leaf crumpling, 3= moderate leaf crumpling, and 4= severe leaf crumpling) were taken on 21, 28, and 31 August and on 4 September. Leaf and petiole samples from each plot were sent to the Plant Pathology Department at UC Davis to confirm the presence of CLCV by squash and dot blot hybridization with a general DNA probe, which detects the presence of whitefly transmitted geminiviruses and DNA sequencing of a polymerase chain reaction amplified fragment from an infected plant confirmed that the geminivirus was CLCV.
Results showed that there were differences in whitefly infestation levels and virus disease symptoms among the cotton entries in this study. The experimental cotton breeding-line C95387 had a lower CLCV disease symptom rating (1.1) (p # 0.05, SNK) than other entries in the study and no CLCV was detected through by squash and dot blot hybridization with a general DNA probe. The experimental cotton breeding-lines C95383 and C95483 had a lower CLCV disease symptom rating (2.2 and 2.1 respectively) (p # 0.05, SNK) than other entries in the study except C95387. The cotton cultivar Stoneville 474 had a higher CLCV disease symptom rating (3.7) (p # 0.05, SNK) than other entries in the study.
Investigator's Name(s): E. T. Natwick1, C. C. Chu2, T. J. Henneberry2, D. Brushwood3, & G. Constable4.
Affiliation & Location: 1University of California Cooperative Extension, University of California Desert Research and Extension Center, 1050 E. Holton Road, Holtville, CA 92250, 2USDA-ARS, Western Cotton Research Laboratory, Phoenix, AZ, 3USDA-ARS Cotton Quality Research Station, Clemson, SC and 4CSIRO, Narrabri, NSW Australia.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: March - December 1998
Silverleaf Whitefly Infestation Levels on Normal Leaf and Okra-Leaf Upland Cotton Cultivars
Sixteen upland cotton, Gossypium hirsutum L., cultivars and experimental breeding-lines were evaluated in the field for susceptibility to silverleaf whitefly, Bemisia argentifolii Bellows and Perring, sown at the UC Desert Research & Extension Center, Imperial Valley, CA, into plots of a randomized complete block design experiment replicated four times, and irrigated 25 March, 1998. The normal leaf cultivars were DP 20, DP 50, DP 90, DP 5415, DP 5432, DP 5461, DP 9775, DP5557, Stoneville 474, and Texas 121, and the okra-leaf cultivars and breeding-lines were Siokra L23, FiberMax 832, FiberMax 819, FiberMax 975, CSIRO 91212-265, and CSIRO 89230-244-1028. Individual plots measured 14 m in length with 4-beds on 1 m centers. No insecticides were applied to the cotton plots. Silverleaf whitefly adults were sampled from ten plants at random in each plot via the leaf turn method using the 5th main stem leaf from the terminal on 10, 17 June, 7, 14, 21, 28 July, 4 & 12 August, 1998. Silverleaf whitefly eggs and nymphs were counted on 1.54 cm2 leaf disks of from ten 5th position leaves down from the terminal extracted from randomly selected plants in each plot on 10, 17 June, 7, 15, 21, 28 July, 4 & 12 August, 1998. Seed cotton was hand picked from 0.002 acre per plot and yield data were recorded on 27 August, 1998. The okra-leaf entries as a group had fewer silverleaf whitefly adults, eggs and nymphs than the normal leaf cotton entries. Siokra L23 had the lowest numbers of silverleaf whitefly adults, eggs and nymphs among the okra-leaf entries. There were no differences in seed cotton yield among the entries, p # 0.05, SNK.
Investigator's Name(s): David P. Puthoff, T. M. Perring & L. L. Walling.
Affiliation & Location: Depts. of Botany and Plant Sciences and Entomology University of California, Riverside, CA 92521.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: 1998
Plant-Insect Interactions: the Defense Reaction of Tomato to Whitefly Feeding
Silverleaf whiteflies have devastated agricultural crops across the southern United States and throughout the world. This phloem-feeding insect not only transmit many plant viruses but also causes several developmental disorder. These disorders range from irregular ripening of tomatoes to silvering of squash leaves. Many of these disorders lead to unmarketable products. Although plant-insect interactions are a major part of the study of plant defense mechanisms, little is known about how plants respond to phloem-feeding insects. Most studies in plant defense have concentrated on either plant wounding, or virus and bacterial infection. Therefore, plant-defense responses to whitefly feeding were monitored. Two-month old tomato plants were infested with either silverleaf (B. argentifolii) or greenhouse (T. vaporariorum) whiteflies. After nine days of infestation the infested and upper non-infested leaves were harvested. These leaves were used for Northern blot analysis using radioactively labeled probes from several pathogenesis-related (PR) genes (PR1a, glucanases, chitinases, etc.), and several wound-induced genes (Lap, pin1, pin2). Whitefly feeding induced the accumulation of the PR gene mRNAs, but not mRNAs from genes regulated by the octadecanoid pathway. We have also used the technique RNA differential display to clone novel genes that are induced following whitefly feeding. After surveying many potential clones we have chosen to focus on one gene that has very high similarity to potential NADPH oxidases from other plant species. This gene (Wfi1) was induced after either species of whitefly had been feeding for 9 days. Wfi1 is also induced following ethylene treatment and treatment with methyl jasmonate. However, it is not induced following drought, salt stress or by ABA or by systemin treatments. Continued characterization of this gene and its protein product are underway in the hopes of understanding what role it might play in the larger scheme of plant defense.
Investigator's Name(s): W. T. G. van de Ven, T. M. Perring, & L. L. Walling.
Affiliation & Location: University of California, Riverside, CA.
Research & Implementation Area: Section E: Host-Plant Resistance, Physiological Disorders, and Host-Plant Interactions.
Dates Covered by the Report: To January 1999
Genes Modulated in Silverleaf Whitefly Infested Squash
Using RNA differential display we identified 2 genes which are modulated in squash by silverleaf whitefly
(Bemisia argentifolii) infestation.
SLW1 and SLW3 are specifically induced in the infested and silvered leaves 3-4 weeks
after infestation with silverleaf whiteflies. These genes are not induced or are induced to a much lesser extent in
squash leaves infested with sweetpotato whiteflies
(Bemisia tabaci biotype A) or non-infested leaves.
SLW1 and SLW3 appear not to be induced by adult whitefly feeding. Both wounding and exogenously applied methyl jasmonite induced
the expression of SLW1.
SLW1 was also expressed during flower development independent of infestation with
whiteflies, while SLW3 was not expressed in flowers.
SLW1 and SLW3 were further characterized by hybridization,
sequence analysis and functional complementation. SLW1 encodes a 54 kD protein and has high similarity to proteins
belonging to the M20B peptidase family, which are involved in hydrolyzing peptic bonds.
SLW3 encodes a 55 kD protein which has a high similarity to cyanogenic (-glucosidases, involved in plant defense responses to tissue damage.
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