Screening Luffa germplasm and advanced breeding lines for resistance to Tomato leaf curl New Delhi virus

The two cultivated Luffa species can be severely infected by Tomato leaf curl New Delhi virus (ToLCNDV) with up to 100% yield loss. Here, 52 Luffa genotypes were screened for ToLCNDV resistance after natural field infection. Mean vulnerability index (VI) ranged from 0.00 to 75.33; genotypes IIHR-137 and IIHR-138 had no symptoms (VI 0), 16 genotypes were resistant (VI 0–25), 15 were moderately resistant (VI 26–50), and 19 were moderate to susceptible (VI?>?50). Ten of the most resistant genotypes and five susceptible checks were then challenge-inoculated using whiteflies or sap in an insect-proof net house; only IIHR-137 [L. cylindrica (L.) Roem.] was symptomless (VI 0.00), and 3–5% of plants of IIHR-138 [L. cylindrica (L.) Roem.] and IIHR-Sel-1 [L. acutangula (L.) Roxb.] had only mild symptoms; genotype Arka Prasan was most susceptible (VI 80.96). Asymptomatic plants were confirmed as infected using polymerase chain reaction. Susceptible genotypes rapidly developed leaf curling, then a severe mosaic 10 days post-inoculation. The resistant inbred lines identified are good candidates for a breeding program for ToLCNDV-resistant cultivars.

     

Studies on the broodstock production and larval rearing of Coral demoiselle Neopomacentrus nemurus (Bleeker 1857)

Steps taken for broodstock development of Neopomacentrus nemurus, Coral demoiselle (Bleeker, 1857) in a hatchery, its spawning and development of egg to the juvenile stage are described. Among the three treatments tried, only the trial using Parvocalanus crassirostris nauplii as the first diet helped in the development of larvae. Larval and post‐larval growth was studied for a period of 65 days post hatch. The larva measured 2–2.4 mm in total length at the time of hatching. The mouth size of larva at the time of hatching measured 237.92 µm. By the 5th day, the width of the larval body had significantly increased. All the fins were conjoined, except for the caudal fin which had begun its appearance on the 2nd day itself. The digestive system was functional by the 5th day and the copepod remains were seen in the digestive tract. The larva metamorphosed by the 15th day with fully developed fins and fin rays. On the 20th day, the larval body had begun to display signs of fin pigmentation. The larva assumed adult pigmentation by the 35th day. By the 65th day, the larva grew to a total length of about 27 mm and weighed about 0.56 g.     

Genetic analysis of resistance to watermelon bud necrosis orthotospovirus in watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai]

An experiment was conducted to study the genetics and nature of gene action of resistance to watermelon bud necrosis orthotospovirus (WBNV) in watermelon. The experimental materials comprised of two resistant (BIL‐53 and IIHR‐19) and one susceptible (IIHR‐140) parents. Each of the resistant parents was crossed with the susceptible parent to develop six generations (P1, P2, F₁, F₂, BC1 and BC2) to study genetics. The results of segregation in F₂ and backcross progenies suggested that resistance is governed by a major dominant gene along with other background minor genes in both the crosses. BIL‐53 was found to possess higher degree of resistance with simple inheritance and hence may be of interest to breeders. Simple selection can be effective for improving the trait in the cross BIL‐53 × IIHR‐140 as additive gene action is prevalent.     

Generation mean analysis of resistance to downy mildew in adult muskmelon plants

Downy mildew (Pseudoperonospora cubensis) is the most devastating disease in muskmelon (Cucumis melo). A generation mean analysis study was designed to determine the types of gene action and estimate the heritability for resistance to downy mildew in four selected crosses of muskmelon. Generation mean analysis revealed that genetic dominance may be of greater importance for expression of resistance to downy mildew in both greenhouse and field experiments and in all the crosses. The F₁ mean was significantly lesser than the mid-parent value and skewed towards resistant parent in all the crosses. Negative sign associated with gene effects indicated, in those crosses, that disease level could be decreased in relation to midparent. All the crosses expressed significant and positive additive (d) gene effects. Dominance (h) and dominance × dominance (l) gene effects had opposite sign in all crosses and both experiments, which implied duplicate type of gene action. High mid-parent heterosis in all the crosses indicated strong dominance effects (as combination of parental alleles) for resistance to downy mildew. In all the crosses, both resistant and susceptible parent contributed one or more dominant/partially dominant factors for resistance. Estimates of broad-sense heritability were high and relatively consistent in both experiments. The two different screening experiments showed that fixable gene effects (d + i) were lower than the non-fixable gene effects (h + l) in all the crosses indicating greater role of non-additive effects in the inheritance of resistance to downy mildew. Resistance to downy appeared to be controlled mainly by dominance effects, therefore the inbred lines IIHR 121 and IIHR 122 could be used strategically to exploit heterotic effects.