Two popular stable restorer lines, CB 87 R and CB 174 R, were improved for blast resistance through marker-assisted back-cross breeding (MABB). The hybrid rice development program in South India extensively depends on these two restorer lines. However, these restorer lines are highly susceptible to blast disease. To improve the restorer lines for resistance against blasts, we introgressed the broad-spectrum dominant gene Pi54 into these elite restorer lines through two independent crosses. Foreground selection for Pi54 was done by using gene-specific functional marker, Pi54 MAS, at each back-cross generation. Back-crossing was continued until BC₃ and background analysis with seventy polymorphic SSRs covering all the twelve chromosomes to recover the maximum recurrent parent genome was done. At BC₃F₂, closely linked gene-specific/SSR markers, DRRM-RF3-10, DRCG-RF4-8, and RM 6100, were used for the identification of fertility restoration genes, Rf3 and Rf4, along with target gene (Pi54), respectively, in the segregating population. Subsequently, at BC₃F₃, plants, homozygous for the Pi54 and fertility restorer genes (Rf3 and Rf4), were evaluated for blast disease resistance under uniform blast nursery (UBN) and pollen fertility status. Stringent phenotypic selection resulted in the identification of nine near-isogenic lines in CB 87 R × B 95 and thirteen in CB 174 R × B 95 as the promising restorer lines possessing blast disease resistance along with restoration ability. The improved lines also showed significant improvement in agronomic traits compared to the recurrent parents. The improved restorer lines developed through the present study are now being utilized in our hybrid development program.

Banana bunchy top virus (BBTV) is one of the major viruses causing high yield loss in bananas. The study was carried out to gain a better understanding of the host and virus interaction and to explore the adaptive mechanism and biochemical responses in banana cultivars viz., Rasthali and Grand Naine against the banana bunchy top virus (BBTV). In the leaf samples of BBTV infected Rasthali and Grand Naine, estimated the total chlorophyll, carbohydrates, phenols and enzyme activities such as peroxidase, polyphenol oxidase, catalase, ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase. The virus infected samples of both cultivars showed a significant increase in the defense enzymes over the healthy sample. Higher total phenols in healthy Rasthali plants which further significantly increased after BBTV infection was observed in comparison to Grand Naine. In contrast to Grand Naine, Rasthali showed higher polyphenol oxidase (PPO) activity contributing to increased polyphenol content. Higher superoxide dismutase (SOD) activity in virus infected Rasthali was observed in comparison to Grand Naine. The increased amount of total phenols, polyphenols and SOD activity in Rasthali might have contributed to less susceptibility to bunchy top virus. However, total protein and chlorophyll content were reduced after BBTV infection in both the banana cultivars.

Background-Bacterial leaf blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive diseases affecting rice production worldwide. Resistance breeding is considered a durable, effective, and eco-friendly approach to control BB. Several BB resistance (R) genes have been identified that confer resistance against various strains of Xoo. The dynamic nature of this pathogen needs proper knowledge of pathotype composition and its virulence among the diverse Xoo strains which is imperative for designing a resistance breeding program. Methods-In this study, we conducted an extensive survey to collect BB infected samples from diverse rice-growing regions of Tamil Nadu. Further, the samples were identified as Xoo through morphological and molecular identification methods. The pathotyping and virulence profiling of Xoo isolates was carried out on a set of rice differentials consisting of 22 near-isogenic lines (NILs) of IR24 possessing different BB resistance genes under glasshouse conditions during Kharif 2021-2022. Results-Based on the disease reaction in 22 rice BB differentials (IRBB lines), the Xoo isolates were grouped into six pathotypes (I II, III, IV, V, and VI). Further, the virulence analysis revealed that the near-isogenic lines possessing single R gene and gene pyramids were susceptible to about 20-88% and 4-20% respectively to Xoo isolates. R genes and their pyramids such as (Xa7, Xa21, Xa4+xa5+Xa21, Xa4+xa5+xa13 Xa4+xa13+Xa21, xa5+xa13+Xa21, and Xa4+Xa21+xa5+Xa21) were found to be effective against all the pathotypes in Tamil Nadu. The pathotype III was predominantly distributed (40%) over the Tamil Nadu. The isolates found in the pathotypes I and II are more virulent and in the pathotypes V, VI are less virulent. The current study identified the virulence nature of diverse Xoo isolates and the effectiveness of resistance (R) genes against the Xoo isolates. Therefore, the effective R genes identified in this study could be an effective source for resistance breeding program against BB in Tamil Nadu.