Resistant Plant Introductions Research Articles

Evaluation of Resistance to Gummy Stem Blight in a Population of Recombinant Inbred Lines of Watermelon × Citron

Gummy stem blight (GSB), a major disease caused by Stagonosporopsis cucurbitacearum (syn. Didymella bryoniae), has caused significant losses of watermelon in the United States. The lack of progress in the development of resistant cultivars is the result of complex inheritance of resistance and breeding strategies that rely on single-plant selection. Because the sources of resistance are wild watermelon relatives, good fruit quality has been difficult to maintain during the selection process. Three hundred recombinant inbred line (RILs) in a population that carries resistance genes to GSB as well as good fruit quality were produced. This was accomplished by crossing and intercrossing resistant plant introductions, crossing the resulting progenies with elite cultivars, intercrossing those progenies, and, finally, self-pollinating to the S3 generation. The 300 RILs were evaluated for disease severity and fruit morphological and quality traits under greenhouse and field conditions in a randomized complete block design with 10 replications and 3 years. The means and correlations for disease severity ratings and fruit quality traits were estimated. Approximately 186 RILs had disease severity ratings below the mean value of the disease assessment scale (4.5), indicating that they possibly carry one or more genes for resistance to GSB. All disease severity ratings were correlated to each other (r = 0.67–0.98; P < 0.001), but they were not correlated with fruit quality traits. Most importantly, several resistant RILs showed good to excellent fruit quality. Our results provide evidence of improved germplasm with high resistance and good fruit quality.

Analysis and Identification of QTL for Resistance to Sclerotinia sclerotiorum in Pea (Pisum sativum L.).

White mold caused by Sclerotinia sclerotiorum is an important constraint to field pea (Pisum sativum L.) production worldwide. To transfer white mold resistance into an adapted background, and study the genetics of the disease, two recombinant inbred line (RIL) populations (PRIL17 and PRIL19) were developed by crossing two partially resistant plant introductions with two susceptible pea cultivars. PRIL17 (Lifter × PI240515), and PRIL19 (PI169603 × Medora) were evaluated for resistance to white mold by measuring lesion expansion inhibition (LEI) and nodal transmission inhibition (NTI) at 3, 7, and 14 days post inoculation (dpi) under controlled environmental conditions. Lesion expansion inhibition percentage (LEIP), survival rate (SR), and area under disease progress curves (AUDPC) were also calculated accordingly. Because of a positive correlation between LEI and NTI with height, short and long internode individuals of each population were analyzed separately to avoid any confounding effect of height to pathogen response. A total of 22 short genotypes demonstrated partial resistance based on at least two Porter's resistance criteria. Only two pea genotypes with partial resistance to white mold (PRIL19-18 and PRIL19-124) had both semi-leafless (afila) and short internode traits. Both the RIL populations were genotyped using genotyping by sequencing (GBS). For PRIL17 and PRIL19, genetic maps were constructed from a total of 1,967 and 1,196 single nucleotide polymorphism (SNP) and spanned over 1,494 cM and 1,415 cM representing seven and nine linkage groups, respectively. A consensus map constructed using data from both populations, had 1,486 unique SNPs over 2,461 cM belonging to seven linkage groups. Inclusive composite interval mapping (ICIM) identified thirteen quantitative trait loci (QTL) associated with white mold resistance traits in both populations. Three of them were co-located with height genes (a morphological trait that reduces infection risk and acts as disease avoidance) and the other ten QTL were associated with two forms of physiological resistance (seven for LEI and three for NTI) with LOD and r2 ranging from 3.0 to 28.5 and 5.1 to 64.3, respectively. The development of resistance lines, genetic dissection and identification of markers associated will help accelerate breeding efforts for white mold resistance using molecular breeding approaches.

Identification of Unique Genetic Sources of Soybean Rust Resistance from the USDA Soybean Germplasm Collection

ABSTRACTSoybean [Glycine max (L.) Merr.] rust is caused by the fungal pathogen Phakopsora pachyrhizi. Six rust resistance loci (Rpp1, 2, 3, 4, 5, and 6) have been reported. Crosses were made between 75 resistant plant introductions (PIs) and a susceptible elite line or cultivar. Bulked segregant analysis (BSA) was used to determine if the PI resistance genes mapped to a previously identified locus or to an unreported locus. Fifty‐two PIs had resistance genes that mapped to the Rpp3 region on chromosome 6 of the soybean genome. A set of P. pachyrhizi isolates was used to further characterize the resistance of these PIs. Forty‐two of the PIs exhibited the same reaction profiles as either PI 462312 (Rpp3) or ‘Hyuuga’ (Rpp3 and Rpp5) to the panel of isolates. The fine mapping of Rpp1, Rpp3, and Rpp4 and the availability of the SoySNP50K Infinium Chip data on the USDA Soybean Germplasm Collection made it possible to use BSA and isolate data on these PIs to determine in retrospect how effective haplotype analysis would be in narrowing down the PIs to those likely to have a unique source of resistance. Thirty‐seven of the 52 PIs (71%) mapping to the Rpp3 region had a haplotype identical to that of PI 462312. A combination of these analyses could prove useful in more rapidly narrowing down resistant PIs to those likely to carry a unique resistance gene.

Association between Soybean Cyst Nematode Resistance Loci and Yield in Soybean

Breeding for resistance to soybean cyst nematode (Heterodera glycines Ichinohe; SCN) is an important objective of soybean [Glycine max (L.) Merr.] breeders. There is concern, however, that SCN resistant soybean cultivars yield less than SCN susceptible cultivars under low SCN pressure. This is supported by the report that two quantitative trait loci (QTL) conferring yield depression are linked to the major SCN resistance gene rhg1 on linkage group (LG) G in the resistant plant introduction (PI) 209332. The objective of our study was to test for the association of SCN resistance with yield and other agronomic traits in populations developed from soybean cultivars with resistance derived from PI 88788. We tested five populations of near isogenic lines (NIL) segregating for genetic markers Satt309 or CTA linked to rhg1 and two populations of NILs segregating for Satt431 linked to the resistance QTL cqSCN‐003 on LG J. Population sizes ranged from 23 to 44 NILs, and the populations were yield tested in two years across four locations that had low SCN incidence in previous years. Near isogenic lines predicted to carry the SCN resistance allele yielded significantly (p < 0.05) less than NILs predicted to carry the susceptibility allele in one out of five populations segregating for Satt309 (118 kg ha−1) and in one out of two populations segregating for Satt431 (76 kg ha−1). Significant differences between the two classes of NILs were also observed for plant maturity, plant lodging and plant height in some populations; however, these differences were small in magnitude. Molecular marker data from the NIL populations for the genetic regions flanking the segregating resistance genes suggest the presence of a yield depression QTL distal to rhg1 on LG G and another yield depression QTL linked or pleiotropic to cqSCN‐003 on LG J. Confirmation and refinement of our results will enable soybean breeders to use marker‐assisted breeding to select against yield depressing regions and develop SCN resistant cultivars that compete with SCN susceptible cultivars even under low SCN pressure.

Evaluation of Soybean Resistance to Sclerotinia Stem Rot Using Reciprocal Grafting.

Sclerotinia stem rot of soybean is one of the major soybean diseases in the north central region of the United States. One disease management option is to plant cultivars that have resistance. Some sources of partial resistance have been identified, but information pertaining to the nature of resistance is limited. The objective of this study was to determine if the expression of resistance is dictated by shoots of resistant plants and if this can be altered by using resistant and susceptible soybean genotypes grafted in different shoot and rootstock combinations of self-, single-, or double-shoot grafts. After successful grafts were made, several experiments were conducted using different inoculation techniques and soybean genotypes. In one experiment, cotyledons were inoculated with a plug of fungal mycelium, plants were incubated in a mist chamber for 23 h, and plant survival was recorded over time. Based on seven grafting combinations of cross- and self-grafted plants using two soybean cultivars, grafts with NKS19-90 (partially resistant) as shoots had greater (P ≤ 0.05) plant survival at 3, 4, and 5 days after inoculation than the other graft combinations. In another experiment, a total of 17 graft combinations were generated using resistant plant introductions and two susceptible cultivars. Resistant self-grafts of the plant introductions had greater (P ≤ 0.05) plant survival (mean = 75%) than self-grafts of the susceptible cultivars (mean = 15%) at 5 days after inoculation. Inter-genotypic grafts with resistant shoots had greater (P ≤ 0.05) plant survival (mean = 65%) than those in reciprocal combinations (mean = 8%) 5 days after inoculation. A cut stem inoculation method was used to test graft combinations of one resistant and two susceptible cultivars. Grafts with susceptible shoots of cvs. Williams 82 and Asgrow 2242 had greater (P < 0.05) lesion lengths (mean = 13.2 cm) than shoots of NKS19-90 (mean = 9.2 cm) regardless of the rootstock 15 days after inoculation. In a double-graft experiment, shoots of both NKS19-90 and Williams 82 were grafted to either NKS19-90 or Williams 82 rootstocks. Regardless of the rootstock, the shoots of Williams 82 died while shoots of NKS19-90 survived. For all the experiments, resistance was greater when the grafted shoot came from a resistant source on a susceptible rootstock compared with the reciprocal combination regardless of the type of grafting technique or inoculation method.

A Retrospective DNA Marker Assessment of the Development of Insect Resistant Soybean

There has been limited success over the past 30 yr in the development of superior soybean cultivars [Glycine max (L.) Merr] with insect resistance. Success may be hampered by the quantitative nature of resistance and by linkage drag from resistant plant introduction (PI) donor parents. Soybean insect resistance quantitative trait loci (SIR QTLs) have been identified from PI 229358 and PI 171451 by restriction fragment length polymorphism (RFLP) analysis. The objective of this study was to tag the SIR QTLs from PI 229358 with simple sequence repeat (SSR) markers and to determine the extent to which the SIR QTLs have been introgressed in registered cultivars, germplasm releases, or breeding lines that have resistance derived from this PI or from PI 171451. Marker analysis defined intervals by 5 centimorgans (cM) or less for a SIR QTL on linkage group D1b (SIR‐D1b), and for SIR‐G, SIR‐H, and SIR‐M. SIR QTLs were tracked through pedigrees by evaluating the inheritance of PI alleles at marker loci tightly linked to the QTLs during the phenotypic selection for insect resistance. It was inferred that at least 13 of the 15 SIR genotypes studied had introgressed SIR‐M. PI genome introgression around SIR‐M was measured to assess linkage drag. Some genotypes exhibited a dramatic reduction in the amount of linked PI genome, which likely occurred in response to phenotypic selection for agronomic performance as a means of reducing linkage drag. Only a few genotypes were inferred to possess SIR‐G or SIR‐H, and no genotypes possessed SIR‐D1b. The results of this study indicate that marker‐assisted selection for SIR QTLs is needed to introgress these loci into elite genetic backgrounds.

Molecular Tagging of Gummy Stem Blight Resistance in Watermelon

The fungus Didymella bryoniae causes gummy stem blight (foliar phase) and black rot (fruit phase) in cucurbits. As resistance to other diseases have been incorporated into cucurbits, losses due to gummy stem blight have increased. Populations derived from crosses between a cultivated watermelon (SS-4), susceptible to the fungus Didymella bryoniae and resistant plant introduction accessions (PI 189225 and PI 272778) are used to detect molecular markers linked to gummy stem blight disease resistance. Genomic DNA was purified from primary leaves of watermelon seedlings before seedlings were inoculated with a spore suspension of the fungus. Disease severity was rated 4 days after inoculation. DNA bulked from resistant or susceptible BC seedlings was amplified to detect AFLP markers. Linkages between gummy stem blight resistance and AFLP markers were identified and should facilitate evaluation and selection of watermelon populations segregating for gummy stem blight resistance.

Effect of Antibiotic Plant Resistance on the Reproductive Fitness of the Russian Wheat Aphid (Homoptera: Aphididae)

Laboratory experiments were conducted to examine the effect of antibiosis on the reproductive fitness of the Russian wheat aphid, Diuraphis noxia (Mordvilko ). Cumulative nymphal production was modeled for 6 wheat, Triticum aestivum L., plant introductions (PI 47545, PI 94355, PI 94365, PI 151918, PI 225245, PI 225262) and a susceptible standard, ‘Stephens’ wheat, with a nonlinear regression procedure that used the logistic equation. It was not possible to model the resistant standard, ‘Border’ oat, because of early mortality and lack of nymphipositional activity. The maximum nymphal production (M) ranged from 68.3 (PI 225262) to 87.2 nymphs per female (Stephens wheat). The rate of increase, or increase in nymphal production rate, ranged from 2.4 (PI 225262) to 3.0 (Stephens wheat). The lag time ranged from 2.5 (Stephens wheat) to 2.7 log (days) (PI 151918). Lag time represented the period before the adult female began to produce nymphs. The original time scale (days), was transformed (natural log) to evaluate the early lag phase in these data. Contrasts of parameters M and K , and joint hypothesis testing (comparison of entire curve) among Stephens wheat and the selected resistant plant introduction lines indicated that there were significant differences between Stephens wheat and all plant introduction lines examined for all parameter comparisons ( M, K , and whole curve). Estimated models from trial 1 were applied to data from trial 2 to validate the suitability of the models to describe the nymphal production process. Examination of residuals (defined as the difference between the predicted value and the observed value) suggested that although the models tended to slightly overestimate nymphal production, they adequately represented nymphal production data for all plant introduction lines as well as Stephens wheat.

Feeding Damage of Russian Wheat Aphid on Resistant and Susceptible Wheat Genotypes

Effects of Russian wheat aphid (Diuraphis noxia Mordvilko) feeding on resistant wheat (Triticum aestivum L.) plant introduction line, PI 137739 (antibiotic line), and a susceptible cuitivar, Stephens, were examined. Reduction in leaf chlorophyll content was determined after different densities (0,40 and 80) of aphids were allowed to feed for 3, 6, 9, and 11 days in leaf cages attached to seedlings. In the non-caged region of infested plants, leaf chlorophyll content was significantly higher in PI 137739 compared with Stephens. Reduction in chlorophyll content was not aphid-density or duration of aphid-feeding dependent in the non-caged regions. In the caged region, increased physical damage to leaves and significant reduction in total chlorophyll content were observed in PI 137739 compared with Stephens. Increased aphid density and prolonged aphid-feeding caused greater reduction in leaf chlorophyll content in caged sections. Increased probing of aphids because of restricted movement in the caged section and tissue unpalatibility of the resistant genotype could have caused severe chlorophyll reduction in the resistant plant introduction line, PI 137739.

Identification and Evaluation of Additional Sources of Resistance to Peanut Root-knot Nematode in Arachis hypogaea L.1

Abstract The root-knot nematode (Meloidogyne arenaria race 1) causes significant economic losses throughout the peanut (Arachis hypogaea) production areas of the southern U.S. Chemicals for control of this pest are becoming increasingly limited, and there are no peanut cultivars with resistance. Seven moderately resistant plant introductions have been identified; however, less than 25% of the germplasm collection has been examined for resistance based on nematode reproduction. The objectives of this work were to examine an additional 1000 plant introductions for resistance to the peanut root-knot nematode and to compare the most resistant introductions to previously reported sources of resistance. Preliminary greenhouse screening trials were conducted to rate severity of root galling and amount of egg mass production. Seventeen accessions were selected based on a mean egg mass rating of less than or equal to three. These selections were reevaluated in additional greenhouse and field experiments to quantify levels of resistance and to directly compare these sources of resistance to those previously reported. Eight accessions had a significantly higher level of resistance (lower egg mass rating) than Florunner; however, none had a significantly higher level of resistance than those previously reported. Results of this study identified additional sources of resistance which may provide unique genes for resistance. In addition, two of these new sources of resistance (PI 298848 and PI 311265) exhibited significantly higher yield than those previously identified when grown in soil heavily infested with M. arenaria.

Inheritance of Resistance to the Southern Root‐Knot Nematode in Soybean

The inheritance of resistance to the southern root‐knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] in soybean [Glycine max (L.) Merrill] was determined for crosses of a susceptible cultivar, Bossier, with two resistant plant introductions, PI96354 and PI417444. Each F1, F2, and/or F3 generation was screened in a greenhouse for resistance to gall formation. In the PI96354 × Bossier population the number of galls per F2 plant and F3 family mean gall numbers were continuously distributed. The PI417444 × Bossier F3 family mean gall numbers were also distributed continuously. for both crosses, each F2 and/or F3 distribution indicated that resistance was quantitatively inherited. Variance component heritability estimates on a mean and plot basis for both crosses ranged from 0.79 to 0.93. The parent‐progeny (F2‐F3) correlation calculated for PI96354 × Bossier was 0.73. The uniqueness of resistance genes was determined for crosses among ‘Forrest’ (resistant), PI96354, and PI417444. F3 progeny from crosses of PI96354 × Forrest and Forrest × PI417444 exhibited transgressive segregation. Individual F3 plants and F3 families were identified with more galls than Forrest, PI96354, and PI417444. Some F3 plants had the same number of galls as Bossier, the susceptible check. These data indicate that Forrest differs from PI96354 and PI417444 for resistance to M. incognita by at least one gene. for PI96354 × PI417444, the similarity of F1, F2, and parental means and variances indicated that PI96354 and PI417444 have resistance genes at the same loci. Soybean breeders can use this information to develop strategies for using these plant introductions to improve the level of M. incognita resistance in adapted cultivars.

Genetic Relationships among Plant Introductions for Resistance to Soybean Cyst Nematode Race 5

Three soybean [Glycine max (L.) Merr.] plant introductions (PI) 399061, PI 424595, and PI 438342 were recently identified as resistant to Race 5 of the soybean cyst nematode (SCN) Heterodera glycines Ichinohe. Plant breeders need to know if these plant introductions have the same or different genes for resistance than those in previously identified resistant plant introductions. Crosses were made between the Race 5 resistant plant introductions and progenies were tested for segregation for resistance to the nematode. Crosses between the three plant introductions and susceptible ‘Tracy‐M’ soybean were made to estimate the number of genes involved in resistance to SCN Race 5. There was no segregation in F3 progenies in crosses among resistant PI 424595, PI 438342, ‘Peking’, PI 90763, and PI 437654. A few susceptible progenies were found from crosses of resistant genotypes ‘Cordell’ or PI 399061 with the other resistant genotypes. All the resistant genotypes appear to have the same genes for SCN Race 5 resistance at most loci, but P1 399061 probably differs in resistance genes from other resistant genotypes at one or more loci. Data from crosses of Tracy‐M with P1399061, P1424595, and P1438342 indicate resistance is controlled by three or more genes.

Feeding Behavior of the Russian Wheat Aphid (Homoptera: Aphididae) on Wheat and Resistant and Susceptible Slender Wheatgrass

Russian wheat aphid, Diuraphis noxia (Mordvilko), poses a serious threat to the yield and quality of wheat ( Triticum aestivum L.) and barley ( Hordeum vulgare L.) production in the United States. Although, Land Grant College and Soil Conservation Service programs advocate the use of many cool- and warm-season forage grasses, many of these grasses serve as alternate hosts to the Russian wheat aphid. One form of cultural control is the development of grass cultivars resistant to Russian wheat aphid for use in such programs, which could eliminate oversummering host plants for the aphid. Prior studies have indicated that slender wheatgrass ( Elymus trachycaulum (Link) Gould ex Shinners), a species commonly found in reclamation areas, offers several potentially resistant plant introductions for use in development of resistant cultivars. The nature of Russian wheat aphid resistance at the behavioral level was studied with four slender wheatgrass entries, ‘Pryor’, PI 387888, PI 440100, and PI 440102 and ‘TAM W-101’ wheat on electronic feeding monitors. Aphids on the resistant plant introductions and, to a lesser degree, on ‘Pryor’ spent more total time engaged in baseline behavior, less time in phloem-ingestion behavior, and more time in nonphloem-ingestion behavior than did aphids on the susceptible entries ‘TAM W-lOl’ wheat and slender wheatgrass PI 387888. These results indicate that PI 440100 and PI 440102 could be used in the development of slender wheatgrass cultivars resistant to Russian wheat aphid.

Mexican Bean Beetle (Coleoptera: Coccinellidae) Development on Resistant and Susceptible Soybean Lines in the Laboratory and Relationship to Field Selection

Laboratory investigations were conducted to study development and mortality of Mexican bean beetle, Epilachna varivestis Mulsant, larvae reared on resistant plant introduction lines, released field-screened resistant breeding lines, and susceptible soybean cultivars. Mortality was low and development normal on susceptible cultivars, indicating an absence of any antibiotic mechanisms. Conversely, high mortality and slower developmental rates of larvae on the various resistant lines indicated presence of antibiotic mechanisms. Antibiosis was apparent as three relative levels: low resistance (L76-0328, L76-0049), medium resistance (L76-0272, L76-0038, L78-608), and high resistance (L76-0132, PI 227687, PI 171451, PI 229358). Results also suggest that a larval screening technique conducted specifically for an antibiotic reaction could be as effective as using existing field-screening techniques to develop resistant soybeans with high levels of antibiosis.

Reductions in Consumption., Utilization, and Growth Rate of Soybean Looper (Lepidoptera: Noctuidae) Larvae Fed Foliage of Soybean Genotype PI 227687

Larvae of Pseudoplusia includens (Walker) reared on the resistant plant introduction (PI) 227687 exhibited reduced growth and high mortality relative to those reared on the susceptible cultivar ‘Davis.’ These effects were most pronounced in the last instar and resulted from an acute action on this instar. The plant genotype consumed during instars one through four had no effect on the maximum larval weight attained, pupal weight, or total mortality during larval development, but did affect the duration of larval development. Measurement of food consumption and utilization by larvae of P. includens fed on PI 227687 or ‘Davis’ foliage indicated that reduced growth on PI 227687 was primarily due to feeding deterrence or the lack of feeding stimulation. A lower efficiency of conversion of digested food to body tissue, not attributable to reduced consumption, also contributed to reduced P. includens growth rate on PI 227687.

Multiple Insect Resistance in Several Soybean Genotypes1

Three commercial soybean [Glycine max (L.) Merr] cultivars and two breeding lines were evaluated for levels of resistance to four insect species. ‘Centennial’, ‘Forrest’, and ‘Tracy‐M’ and the advanced breeding lines D75‐10169 and D75‐12035 were compared to the insect resistant plant introduction (PI) 229358 for levels of resistance to velvetbean caterpillar (Anticarsia gemmatalis Hübner), soybean looper [Pseudoplusia includens (Walker)], tobacco budworm [Heliothis virescens (Fabricius)], and corn earworm [Heliothis zea (Boddie)]. Three tests were conducted in two environments. Average weights of lepidopteran larvae reared on leaves from the five genotypes were greater than those reared on leaves from PI 229358 by 6.3, 24.4, 43.3, 73.6, and 92.7% for D75‐10169, D75‐12035, Tracy‐M, Forrest, and Centennial, respectively. Each plant genotype showing resistance to one of the insect species also showed resistance to the other three species evaluated. Thus, the development of cultivars from PI 229358 with resistance to several insect species may be possible without the costly and time‐consuming process of screening each insect species at each selection stage in a breeding program. The use of cultivars with intermediate levels of resistance as adapted parents in crosses with resistant germplasm may facilitate the development of highly resistant and agronomically desirable soybean genotypes.

Recurrent Selection for Resistance to Iron Deficiency Chlorosis in Soybeans1

The objective of our study was to evaluate the use of recurrent selection by S1 testing for development of a soybean [Glycine max (L.) Merr.] population with improved resistance to iron‐deficiency chlorosis on calcareous soil. An intermated population was developed with the 10 most resistant cultivars or experimental lines and the 10 most resistant plant introductions available in 1975. Each cycle of selection required 1 year and included the growing of S0 plants in Puerto Rico during the winter to obtain 100 S1 lines, evaluation of the S1 lines for chlorosis score on calcareous soil in Iowa, selection of the 10 most resistant lines before flowering, and recombination of selected lines for the next cycle of selection. Progress from selection was evaluated by comparing the mean performance of the parents for the cycle 0, 1, and 2 populations on calcareous soil in four Iowa environments.There was a significant linear improvement in mean chlorosis score from cycle 0 to 2. The average genetic gain per cycle and year of 0.2 units was 9% of the cycle 0 mean. The highest frequency of resistant lines was from the cycle 2 parents. Genetic improvement in the population indicated that resistance to iron‐deficiency chlorosis is influenced by genes with additive effects. The results also indicated that early‐generation testing of F2‐derived or S1 lines should be effective in development of cultivars with the desired level of resistance.

Inheritance of Resistance to Race 2 Anthracnose in Watermelon1

Abstract Inheritance of resistance to Colletotrichum lagenarium (Pass.) Ell. &amp; Halst. race 2 in watermelon (Citrullus lanatus (Thunb.) Matsum &amp; Nakai) was determined in progeny from crosses between resistant plant introductions (PIs) 189225, 271778, and 326515 and susceptible cultivars ‘Charleston Gray’, ‘Jubilee’, ‘Crimson Sweet’ and AWB-10 advanced line. Parents and progenies were screened for resistance in field and greenhouse plantings. Resistance of F1 plants indicated resistance was dominant. The F2 plants segregated 3 resistant: 1 susceptible. The backcross of the F1 to the susceptible parent segregated 1:1. Resistance in all Pis tested was controlled by a single dominate gene pair.

Soybean Resistance to the Southern Green Stink Bug, Nezara viridula12

In 1973,654 soybean lines were field-screened for resistance to pentatomid pests in South Carolina. Twenty-seven lines were selected and tested in 1974 in replicated field plots. None was highly resistant under heavy feeding pressure by Nezara virudula (L.), Acrosternum hilare (Say), and Euschistus spp., with seed damage ranging from 30.2 to 84.2%. Five of these lines and 3 insect resistant plant introductions (PIs) 171451, 227687, and 229358 were tested for development, mortality, and weight gain of N. viridula nymphs confined over pods in the field and under laboratory conditions. All 3 PIs exhibited resistance to N. viridula in 2 or 3 of the forced-feeding tests. PI229358 was the most consistently resistant in all tests, causing significantly higher mortality, longer development, and lower weight gain for nymphs compared to those on ‘Bragg’. The performance of some of the breeding lines was variable among the tests but showed that the resistance can be transferred by crosses with commercial cultivars.

‘Vanguard 75’ Lettuce1

Abstract Lettuce mosaic virus (LMV), has been one of the most destructive diseases of lettuce (Lactuca sativa L.) in nearly all production areas of the world. One of the major goals of the USDA Lettuce Breeding Project in Salinas, California, has been to develop mosaic resistant cultivars. We began this program in 1959 with a search for sources of resistance. Three years later, we identified 3 resistant Plant Introductions from Egypt (3).