​Screening of Pigeonpea Varieties through Nylon Bag No-choice Bioassay for Host Plant Resistance to Helicoverpa armigera

Background: The legume pod borer, Helicoverpa armigera (Hübner), is one of the most damaging crop pests, including pigeonpea. Host plant resistance is a component of pest management and therefore, we standardize a nylon bag No-Choice Bioassay technique to screen for resistance to H. armigera under field conditions. Methods: Pigeonpea plants were infested with 24 h old 1, 2, 3, 4 and 5 larvae per plant inside the nylon bag. Observations were recorded on pod damage, larval survival, larval weight, pupation, adult emergence, and fecundity after 10 days. Result: Pigeonpea varieties AL-201, H03-41 and PAU-881 exhibited lower pod damage (15.89 to 19.77%) and larval weight (12.02 to 13.82 mg). The expression of resistance to H. armigera was associated with trichome density, pod wall thickness and higher amount of phenolic compounds and condensed tannins. Lower trichome density and thin pod walls and higher amounts of sugars rendered the varieties Paras, Manak and Pussa-992 more susceptible to H. armigera. Nylon bag assay can be used to screen and select pigeonpea cultivars for resistance to H. armigera.

Heritable Variation, Genetic and Phenotypic Correlations for Tuber Traits and Host Plant Resistance to Late Blight for Potato Breeding in Scandinavian Testing Sites

Potato breeding aims to improve crop productivity, quality and resilience based on heritable characteristics. Estimating the trait heritability and correlations—both genetic and phenotypic—among characteristics in a target population of environments allows us to define the best breeding method that leads to selection gains. Breeding clones (47) and released cultivars (209) were grown using simple lattice designs at three testing sites in northern and southern Sweden to estimate the best linear unbiased predictors (BLUPs) derived from mixed linear models for characteristics such as tuber weight (total and according to sizes), host plant resistance to late blight (caused by the oomycete Phytophthora infestans) and tuber quality (starch percentage based on specific gravity measurements and reducing sugars). There was significant heritable variation for all the characteristics investigated. Tuber starch percentage and total tuber weight were the traits with the highest broad-sense heritability (H2), while the weight for the smallest size (<40 mm) had the highest H2 among the different tuber categories. These results show the potential for further improving these traits for Scandinavia through recombination and selection in segregating offspring. The genetic and phenotypic correlations among the tuber weight characteristics were significant (p ≤ 0.05) irrespective of their sizes, but none were significant (p > 0.05) with tuber starch percentage. Host plant resistance to late blight was negatively and significantly associated with tuber weight and starch percentage, thereby showing the strong effects of this disease on the productivity and quality of the potatoes.

Global patterns of cereal diseases and the impacts of breeding for host plant resistance

Plant breeding for host plant resistance to pathogens brings together different disciplinary domains, especially genetics and plant pathology. The strategies underpinning plant breeding have therefore, logically, been influenced by a number of paradigms that have dominated the field of disease management. This chapter provides a brief overview of these paradigms, where the authors link the implications for plant breeding. In doing so, the authors try to follow an approximate (1) linear and (2) chronological order. Yet the authors are aware that, depending on the considered crop and region, (1) there might have been occasional jumps and step-backs leading to non-linear paths, and (2) the chronology of events may have much varied.

Bio-control of Stem Rot in Jerusalem Artichoke (Helianthus tuberosus L.) in Field Conditions

Stem rot is a serious disease in Jerusalem artichoke (JA). To reduce the impact of this disease on yield and quality farmers often use fungicides, but this control method can be expensive and leave chemical residues. The objective of this study was to evaluate the efficacy of two biological control agents, Trichoderma harzianum T9 and Bacillus firmus BSR032 for control of Sclerotium rolfsii under field conditions. Four accessions of JA (HEL246, HEL65, JA47, and JA12) were treated or notreated with T. harzianum T9 and B. firmus BSR032 in a 4 × 2 × 2 factorial experiment in two fields (environments), one unfertilized and one fertilized. Plants were inoculated with S. rolfsii and disease was evaluated at 3-day intervals for 46 days. T. harzianum T9 and B. firmus BSR032 reduced disease incidence by 48% and 49%, respectively, whereas T. harzianum T9 + B. firmus BSR032 reduced disease incidence by 37%. The efficacy of T. harzianum T9 and B. firmus BSR032 for control of S. rolfsii was dependent on environments and genotypes. The expression of host plant resistance also depended on the environment. However, HEL246 showed consistently low disease incidence and severity index in both environments (fertilized and unfertilized). Individually, T. harzianum T9, B. firmus BSR032, or host plant resistance control stem rot caused by S. rolfsii in JA. However, no combination of these treatments provided more effective control than each alone.

Evaluation of Pigeonpea Genotypes against Fusarium Wilt and Sterility Mosaic Disease in Gujarat

Background: Fusarium wilt (FW) and sterility mosaic disease (SMD) are two important biotic constraints to pigeonpea production worldwide that can cause loss up to 100 per cent. Host plant resistance is the most durable and economical way to manage these diseases. Methods: Thirty five pigeonpea genotypes comprises [mid early, mid late, dual and hybrid (mid early) group] were evaluated in a fusarium wilt and sterility-mosaic disease-screening nursery at three location viz., Sardarkrushinagar, Bharuch and Vadodara in Gujarat during kharif season 2015-16, to identify genotypes having resistance to both the diseases. Result: Five genotypes identified in each group of pigeonpea viz; mid early (SKNP1303, SKNP 1021, SKNP 0805, SKNP 0920, SKNP 1004), mid late (SKNP 1233, SKNP 10-34, AAUVT 07-10, AAUVT 09-24, GJP1207) and dual (SKNP-1119, BP 06-33, BP 08-06, BP 10-03, BP 10-04) and in hybrid (mid early) group only one hybrid i.e. SKNPCH 1211 were found combined resistance to Fusarium wilt and SMD ( less than 10% disease). These diverse genotypes that are resistant to Fusarium wilt and SMD may be useful in pigeonpea disease resistance breeding programme while hybrid identified as resistance to both the diseases may be recommended for commercial cultivation.

↵​Study of Morpho-physiological and Biochemical Traits for Resistance to Yellow Mosaic Virus (YMV) in Blackgram [Vigna mungo (L.) Hepper] Varieties

Background: Blackgram is one of the most important pulse crop in India and it is being affected by a number of insect pests from seedling stage to maturity. Among them whitefly is an important insect pest that transmit the viral disease, yellow mosaic virus (YMV), which is a major disease resulting in severe yield losses accounting for about 70% and infection at early stages may result in complete failure of the crop causing huge loss to the farmers economically. To overcome the losses due to this important disease in blackgram, study of host plant resistance to whiteflies, thereby minimizing the losses due to YMV disease is of great importance. The trichome density plays an important role as a morphological anti-feedant which reduces the pest attack and subsequently lowers the disease incidence and the plants with high trichome density showed less YMV symptom. The morpho-physiological and biochemical traits play an important role in host plant resistance against YMV disease through insect vector resistance and hence, the study was undertaken. Mathods: A field experiment was conducted during rabi 2017-18 and 2018-19 at RARS, Lam, Guntur in a randomized block design with eight blackgram varieties and replicated thrice under receding soil moisture condition. The experiment was conducted using eight blackgram varieties (LBG 787, GBG 1, TBG 104, LBG 884, LBG 806, LBG 808, LBG 623 and LBG 752) obtained from RARS Lam, Guntur and the variety LBG 623 was considered as a susceptible check. The estimation of sugars, phenols, tannins, trichome density and SCMR was done at vegetative and reproductive stages of crop growth. Result: A significant variation was observed among the varieties for all the traits observed at vegetative and reproductive growth stages during both rabi 2017-18 and 2018-19. The total sugar content of the blackgram varieties varied from 25.16 to 49.82 mgg-1 FW; the leaf phenolic content values ranged from 10.26 to 23.55 mg g-1 FW and the tannins content of the dried leaf samples ranged from 0.014 to 0.052 mgg-1 DW. The trichome density of the blackgram varieties varied from 12.91 to 74.59/cm2 of leaf area and the SCMR values ranged from 24.21 to 55.17. Higher seed yield was recorded in the variety LBG 884 followed by GBG1 and the lower seed yield was recorded in the variety LBG 623 during rabi 2017-18 and 2018-19. The YMV resistant varieties showed relatively higher phenolic, tannins content and trichome density and lower total sugar content in the leaf. The total sugar content showed a significant negative correlation with the seed yield. The SCMR value was significantly lower in the susceptible varieties of blackgram with higher disease scores.

Characterization of Strawberry Host Plant Resistance to Powdery Mildew caused by Podosphaera aphanis

Host plant resistance is an essential tool in plant disease management worldwide. Evaluations of strawberry cultivar resistance to powdery mildew were done previously in California, but many new cultivars have been released since the last evaluation in 1996 and merit evaluation for today’s growers. Two studies were conducted over the winter and summer of 2020, evaluating ten commonly grown cultivars. Powdery mildew-free plants were established in 3 L pots under high plastic tunnels and after three weeks (four- to five-leaf stage) moved into a powdery mildew-infested greenhouse. Disease incidence and severity ratings were taken weekly beginning at the first sign of disease. Ratings taken at 40 (winter) and 41 (summer) days after transfer to the greenhouse were used to make comparisons among cultivars. Significant differences were found in foliar disease severity among cultivars, but none were totally free of disease. Moderately resistant cultivars were ‘San Andreas’ and ‘Sweet Ann’. Highly susceptible cultivars were ‘BG 3.324’ and ‘Royal Royce’. Two field evaluations of the ten cultivars confirmed the observed relative differences in host resistance under field conditions. This information is valuable to California strawberry growers who select cultivars based in part on their susceptibility to economically important diseases such as powdery mildew.