Combining yield and leaf curl-mosaic complex virus tolerance in Chilli

Abstract

Chilli (Capsicum spp.) is a widely cultivated crop in India, valued for its economic and culinary significance as vegetables, spices, and in industrial applications such as the production of oleoresins. It is grown for its fresh green and dried red fruits. India is one of the largest producers, consumers, and exporters of chilli, with major growing states including Andhra Pradesh, Telangana, Karnataka, Tamil Nadu, and Maharashtra. Despite its significance, chilli production in India faces several challenges, primarily due to the prevalence of diseases that adversely affect yield and quality. Chilli Leaf Curl Mosaic Complex (CLCMC) is one of the most severe viral diseases affecting chilli (Capsicum spp.) production, especially in tropical and subtropical regions like India. This disease results from a synergistic interaction between multiple viruses, primarily the Chilli leaf curl virus (ChiLCV), a member of the Begomovirus genus, often in association with Tomato leaf curl virus (ToLCV), and sometimes with other satellite molecules or helper components. In severe cases of disease infection, up to 100 percent loss in marketable yield has been reported. Hence, a study entitled ‘combining yield and leaf curl mosaic complex virus tolerance in chilli’ was carried out in the Department of Genetics and Plant Breeding, College of Agriculture, Vellayani during 2020-2024, with the objective of identification of superior cross combinations for leaf curl-mosaic complex virus tolerance, yield and yield attributes in chilli. In the first experiment, a total of sixty-four genotypes, collected from National Bureau of Plant Genetic Resources, Kerala Agricultural University and farmers’ field were screened for natural incidence of chilli-leaf curl-mosaic complex disease in cubic lattice design during the summer of 2023. The highest mean yield per plant (g) was shown by Paal Mulaku (Kumarichanda Local). The genotypes showed significant differences for all the traits under study indicating the presence of substantial genetic variability. These sixty-four genotypes were classified into nine clusters based on Euclidean2 method. A modified disease scoring scale of zero to five was developed for leaf-curl mosaic complex disease by combining the disease scores of chilli leaf curl and cucumber mosaic virus. Disease incidence and severity calculated as vulnerability index were calculated based on disease scoring. The genotypes were classified into immune, tolerant, highly resistant, resistant, susceptible and highly susceptible based on the vulnerability index. Ten genotypes showed immune reaction, while twenty showed tolerance to CLCMC. Hence, a total of thirty genotypes were selected for artificial screening against CLCMC in pot culture experiment. Graft transmission technique was adopted for artificial inoculation during experiment II. The viruses were transmitted from the diseased Vellayani Athulya, used as scion, to the genotypes selected from experiment I, used as rootstocks. Six out of the eleven genotypes that were found to be immune to the disease complex belonged to the top ten high yielding genotypes. Hence, genotypes namely, Venjaramood Local II, KD 2, Unda Chilli (Vadakara Local), AP-1, IC-208580 and IC-570376 were selected as parents for the hybridization program to combine high yielding character and tolerance to chilli leaf curl-mosaic complex disease. Of these the genotype IC-208580 belongs to C.frutescens and Venjaramood Local II, KD-2, Unda Chilli (Vadakara Local), AP-1and IC-570376 belong to C.annuum. The virus titre was estimated based on virus specific primers. No amplification was obtained for the six genotypes when chilli leaf curl virus coat protein specific primer, CLA 7F/CLA 8R was used for the titer estimation while three genotypes showed amplification when degenerate Deng primer was used. This may be attributed to the ability of genotypes to suppress the disease symptom expression. The molecular markers reported to be linked to the diseases were validated in the second part of experiment II. SSR Markers namely PAU-LC-343-1, CA 516044, AVRDC MD*850 and AVRDC-PP188 were reported to be linked to the chilli leaf curl disease resistant gene. SSR Marker HpmsE003 was reported to be linked to cucumber mosaic virus resistance gene. All the markers showed polymorphism between resistant and susceptible genotypes. SSR marker HpmsE003 linked to cmr1 locus, also showed polymorphism between resistant genotypes and susceptible check. The six genotypes were hybridized in a diallel fashion during experiment III. A total of thirty cross combinations were made, with six parents, of which ten cross combinations were interspecific crosses (Capsicum frutescens X Capsicum annuum). Only three of the ten interspecific crosses germinated. Reciprocal crosses: Capsicum annuum X Capsicum frutescens did not germinate. Effectively the total number of crosses was reduced to twenty three. During experiment IV, F1 plants were raised along with their parents for evaluation of yield traits under field conditions with the application of plant protection chemicals and without application of plant protection chemicals for natural disease incidence screening. Vellayani Athulya was used as check variety. All the characters showed non-additive gene action except for fruit girth in the experiment with the application of plant protection chemicals. Highly significant gca effects for fruit weight, number of fruits per plant and yield were shown by the parents Venjaramoodu Local II (P1), IC-570376 (P6) and KD-2 (P2) respectively. High sca effect for number of fruits per plant and fruit yield per plant was shown by the cross combinations, AP-1(P4) x Unda Chilli (Vadakara Local) (P3) and KD-2 (P2) x Venjaramoodu Local II (P1) respectively. Based on mean performance and heterosis the cross combination IC 208580 (P5) x IC-570376 (P6) and Venjaramoodu Local II (P1) x KD-2 (P2) were found superior. Five cross combinations were identified for high yielding character under plant protected conditions while eight cross combinations showed tolerance to leaf curl- mosaic complex disease under natural field conditions. A total of five cross combinations were found to be superior to leaf curl mosaic disease tolerance and yield namely: IC-208580 (P5) x IC-570376 (P6), Venjaramoodu Local II (P1) x KD-2 (P2), KD-2 (P2) x Venjaramoodu Local II (P1), IC-570376 (P6) x KD-2 (P2) and KD-2 (P2) x IC-570376 (P6). The superior cross combinations selected for high yielding capacity along with tolerance to leaf curl-mosaic complex disease can be used in future breeding programs to develop superior high yielding and leaf curl mosaic complex tolerant chilli varieties.