The epidemiology and control of ascochyta blight in field peas: a review

Abstract

Ascochyta blight is one of the most important diseases affecting field peas. The disease occurs in almost all pea-growing regions of the world and can cause significant crop losses when conditions are favourable for an epidemic. Here we review current knowledge of the epidemiology of the disease. Details are provided of disease symptoms, the disease cycle and the taxonomy of the causal fungi, Ascochyta pisi, Mycosphaerella pinodes and Phoma pinodella. The importance of seed-, soil- and air-borne inoculum is discussed along with the factors that influence survival of the causal fungi in soil, on seed or associated with pea trash. Many studies have been reviewed to establish how the fungi responsible for the disease survives from year to year, how the disease becomes established in new crops and the conditions that favour disease development. Evidence is provided that crop rotation, destruction of infected pea trash and chemical seed treatments can significantly reduce the amount of primary inoculum. Later sowing of crops has been shown to reduce the incidence and severity of disease. Fungicides have been used successfully to control the disease, although the cost of their application can significantly reduce the profitability of the crop. The best long-term strategy for effective disease control appears to be the development of ascochyta blight resistant pea varieties. Reports of physiological specialisation in ascochyta blight fungi are also documented. Despite extensive screening of germplasm, relatively few sources of resistance to ascochyta blight fungi have been found in Pisum sativum. However, the discovery of much better sources of resistance in closely related species and the development of advanced breeding methods offer new possibilities for developing useful resistance.

The susceptibility of pea (Pisum sativum L.) to ascochyta blight under Lithuanian conditions

“…It is likely that the major source of pathogens isolated at an early growth stage was seed-borne infection. All pathogens of the Ascochyta complex are seed-borne; M. pinodes and P. pinodella can cause root and foot rots, while first symptoms of A. pisi appear on a stemlet above the first leaves (Bretag et al, 2006). Later, with rapid growth of plants, until flowering stage, the frequency of detection of pathogens of Ascochyta complex diminished, and during flowering-grain formation stage the detection frequency rapidly increased until maturity stage (Table 5).…”

“…Each of these pathogens causes specific symptoms on plants: A. pisi commonly causes leaf and pod spotting, M. pinodes and P. pinodella cause foot and root rots, and on aerial plant parts -stem, leaf and pod spotting (Wallen, 1974). A. pisi symptoms are circular, tan coloured with a dark brown margin, which differ from the multiple brown-purple spots caused by M. pinodes and P. pinodella (Bretag et al, 2006;Chilvers et al, 2009). However, the symptoms of the latter causal agents on the aerial plant part are very similar and difficult to differentiate even with the aid of molecular techniques (Faris-Mokaiesh et al, 1996;Onfroy et al, 1999;Wang et al, 2000).…”

“…However, the symptoms of the latter causal agents on the aerial plant part are very similar and difficult to differentiate even with the aid of molecular techniques (Faris-Mokaiesh et al, 1996;Onfroy et al, 1999;Wang et al, 2000). M. pinodes and P. pinodella infection persists very well on pea residues in the soil; however, the expression of A. pisi saprotrophic properties is weaker, therefore seed infection is more important for the spread of this pathogen (Bretag et al, 2006). The conidia of all pathogens of Ascochyta complex are dispersed by rain-splash in a crop within a short distance; however, M. pinodes ascospores are also wind-dispersed.…”

“…Its causal agents are Ascochyta pisi, Mycosphaerella pinodes, Phoma pinodella, which are often referred to in literature as Ascochyta complex (Onfroy et al, 1999). These pathogens damage plant root, foot and aerial parts, pods and grains (Moussart et al, 1998;Bretag et al, 2006;Marcinkowska, 2008). All three causal agents of ascochyta blight: A. pisi, M. pinodes, P. pinodella are transmitted through infected seed and plant residues in the soil.…”

Dr Maurice Vernon Carter– plant pathologist and epidemiologist, 1926–2014

“…He willingly gave of his time to impart his knowledge and skills in plant disease epidemiology to postgraduate students working on lettuce anthracnose disease, snapdragon rust (Carter et al 1970b), and barley scald (Carter and Banyer 1964) and to other plant pathologists/ disease epidemiologists from other Australian States. His studies provided the framework for extensive studies in Victoria on ascochyta disease of field peas (Bretag et al 2006). He encouraged and supported junior scientists in attending international conferences on mycology and a NATO Advanced Study Institute meeting.…”