Regional characterization of pigeonpea sterility mosaic disease and exploring broad-based resistance

Pigeonpea sterility mosaic disease (SMD) caused by Pigeonpea sterility mosaic virus (PPSMV) is a serious threat to pigeonpea production in the Indian-subcontinent. Recent reports on the possible existence of two different viruses associated with the SMD further complicate the etiology of this difficult to manage viral disease. In this regard, a comprehensive and systematic survey was taken up across several pigeonpea growing areas in southern India to know the disease prevalence and variability in virus isolates. Further, selected pigeonpea elite genotypes were screened in different locations for their broad-based resistance. Results indicate huge variation in SMD incidence among the surveyed states. The highest disease incidence (9.38 percent) was observed in Karnataka, followed by Tamil Nadu state with 8.44 per cent incidence. Andhra Pradesh and Telangana states recorded disease incidences of 4.51 and 2.08 per cent respectively. Samples collected from Patancheru location and tested using viral-specific RNA-3 segment primers were all positive for both the viruses. However, one of the samples collected from Bengaluru location and four samples from Coimbatore location had a positive reaction for PPSMV-2 only. In order to identify broad-based resistance to SMD, 20 pigeonpea genotypes were screened in three different locations (Patancheru, Bengaluru and Coimbatore) in southern-India during rainy seasons of 2017 and 2018. Among them, ICPL- 16078, ICPL-16086 and ICPL-16087 showed resistance reaction ((≤10 % incidence) in all the three locations, whereas, ICPL-16072, ICPL-16077 and ICPL-16083 showed resistance to Patancheru and Coimbatore isolates but highly susceptible (≥40 % incidence) to Bengaluru isolate

First Report of Phakopsora euvitis Causing Leaf Rust Disease on Grapevine (Vitis labrusca) in India

Grapevine (Vitis labrusca L.), a member of the family Vitaceae and native of North America, is grown as a table grape. During the survey for grapevine diseases in May 2022, we noticed numerous yellow pustules of rust on the lower side of leaves of “Bangalore Blue” in Nandi Village (13°22′59.7″N, 77°42′33.4″E), Chikkaballapur District, Karnataka, India. The crop was at the maturity stage, and the rust disease severity was determined using the scale developed by Angelotti et al. (2008), which was up to 10%. The disease symptoms were numerous small, raised yellow pustules on the abaxial surface corresponding to adaxial surface chlorotic spots. In severe conditions, spots cover the entire leaf, and defoliation occurs. Similar disease symptoms were reported by Ono (2000), Primiano et al. (2017), and Weinert et al. (2003)

Salient Findings on Host Range, Resistance Screening, and Molecular Studies on Sterility Mosaic Disease of Pigeonpea Induced by Pigeonpea sterility mosaic viruses (PPSMV-I and PPSMV-II)

Two distinct emaraviruses, Pigeonpea sterility mosaic virus-I (PPSMV-I) and Pigeonpea sterility mosaic virus-II (PPSMV-II) were found to be associated with sterility mosaic disease (SMD) of pigeonpea [Cajanus cajan (L.) Millsp.]. The host range of both these viruses and their vector are narrow, confined to Nicotiana benthamiana identified through mechanical transmission, and to Phaseolus vulgaris cvs. Top Crop, Kintoki, and Bountiful (F: Fabaceae) through mite transmission. A weed host Chrozophora rottleri (F: Euphorbiaceae) was also infected and tested positive for both the viruses in RT-PCR. Among the wild Cajanus species tested, Cajanus platycarpus accessions 15661, 15668, and 15671, and Cajanus scarabaeoides accessions 15683, 15686, and 15922 were infected by both the viruses and mite vector suggesting possible sources of SMD inoculum. Though accession 15666 of C. platycarpus, 15696 of C. scarabaeoides, and 15639 of Cajanus lanceolatus were infected by both the viruses, no mite infestation was observed on them. Phylogenetic analysis of nucleotide sequences of RNA-1 and RNA-2 of PPSMV-I and PPSMV-II isolates in southern India revealed significant divergence especially PPSMV-II, which is closely related to the Fig mosaic virus (FMV) than PPSMV-I. In multilocation testing of pigeonpea genotypes for their broad-based resistance to SMD for two consecutive years, genotypes ICPL-16086 and ICPL-16087 showed resistance reaction (<10% incidence) in all three locations studied. Overall, the present study gives a clear idea about the host range of PPSMV-I and PPSMV-II, their molecular relationship, and sources of resistance. This information is critical for the development of reliable diagnostic tools and improved disease management strategies