Exploration of the genetic resistance to Ascochyta blight in field peas

Abstract

Ascochyta blight (AB) is a disease complex caused by four pathogen species, namely, Didymella pinodes, D. pisi, D. pinodella, and Ascochyta koolunga. Didymella pinodes is the most aggressive and destructive species among the four. A major challenge in resistance breeding is the absence of effective resistance in nature, compounded by the presence of multiple species with different pathotypes, and resistance identified is often species-specific, often resulting in the emergence of other species within the complex when used alone. Furthermore, the coexistence of species on the same plant results in a compromise of single-species resistance. The conventional approach to identifying genes resistant to Ascochyta blight is through screening domesticated peas (Pisum sativum) and the Pisum wild relatives. However, relatives of peas with known levels of resistance are incompatible with domesticated Pisum sativum. Screening techniques in scoring germplasm against AB lack uniformity among the various programs worldwide. To assist phenotyping to find more resistance resources and selection for AB-resistance breeding programs, a high-throughput and reliable AB screening protocol is essential. This study led to the development of optimizing high-throughput Ascochyta blight screening techniques and the identification of resistance to AB. Pathogens in the disease complex interact with one another on a single host plant, with their interspecific interactions significantly affecting disease progression and outcomes. Understanding these interactions is crucial for improving disease management strategies. We investigated the interactions of the pathogens in the complex on a single pea plant. The results revealed a dual dynamic of mutualism and competition over time. D. pisi benefited from the interactions, achieving growth even in immune hosts. In contrast, D. pinodes became more aggressive. Necrotrophic pathogens such as Ascochyta spp. depend on the secretion of cutinases, cell wall-degrading enzymes, cytolytic, and phytotoxic proteins to kill their host cells. Plants do have a defense mechanism of detoxifying toxins released by pathogens, preventing the spread of infection and activating complex defense mechanisms. Understanding the mechanism of host-pathogen interaction will go a long way in identifying genes that confer resistance to Ascochyta blight. The study subjected peas to mutagenesis and subsequently screened against AB.