Screening wild Brassica species against Alternaria brassicicola (Schw.) Wiltsh for breeding Alternaria leaf spot resistance in Brassica vegetables

Alternaria leaf spot is a major disease of Brassica crops, and it causes huge economic loss to both the cultivated Brassica oilseeds and vegetables. The present study was aimed to develop a non-destructive robust method for screening of wild Brassica species and to find resistant wild species against Alternaria brassicicola (Schw.) Wiltsh. For this, 38 wild species of Brassicaceae were screened at adult plant stage by an in vitro detached leaf inoculation method in three consecutive years i.e. 2019–2020, 2020–2021 and 2021–2022. The new screening protocol created favourable environment (temperature 25 ± 2 °C; relative humidity > 90%) for the pathogen by using incubator. The host leaves were retained in turgid condition by placing sucrose 5% w/v on slanting cut at petiolar base. The consistency in reactions of the wild species against A. brassicicola during all three years of testing indicates the robustness of the protocol. Multiple parameters were recorded on leaf condition and disease response of the wild species and devised a score system for disease rating. Complete resistance was observed in Capsella while resistance in Lepidium , Camelina and Biscutella . Both Capsella bursa pastoris (L.) Medik (early) and C. bursa pastoris (late) were symptomless resistant. Camelina sativa (L.) Crantz, Diplotaxis erucoides (L.) DC and Diplotaxis gomez-campoi Mart.-Laborde were found to be resistant against A. brassicicola . The significant correlation between disease parameters indicates the robustness and effectiveness of the screening protocol for wild Brassica species.