Changes in Foliar Host Reaction to Ascochyta Rabiei With Plant Maturity

Abstract

Ascochyta rabiei is the most significant foliar disease of chickpea (Cicer arietinum) worldwide, and can cause both yield loss and reduced seed quality. Significant mean disease score differences were observed from the reactions among a collection of Ascochyta rabiei isolates and chickpea hosts at both seedling and maturity growth stages (P<0.000). Although isolates ranked similarly within their range of pathogenicity at either growth stage, the ranking of host disease reaction was different. This suggests that genotype-specific expression of resistance genes to A. rabiei may be related to growth stage. Hence, durable selection methods for resistance will require screening of isolates representative of the pathogenicity within the population on target genotypes at growth stages representative of the type of resistance being sought, for example seedling resistance or pod resistance.

Evidence and Consequence of a Highly Adapted Clonal Haplotype within the Australian Ascochyta rabiei Population

“…Leaf lesions with no visible pycnidia were surface sterilized and placed on V8 juice growth agar. All agar plates were incubated for 14 days at 22 ± 2°C with a 12/12 h near-UV light irradiation (350–400 nm)/dark photoperiod, and resulting cultures were single spored on V8 juice agar media ( Elliott et al, 2013 ).…”

“…Elliott et al (2013) first detected clones with differing levels of aggressiveness within the Australian A. rabiei population and proposed that despite its clonal nature, the population contained a large potential to evolve and adapt to overcome chemical and host resistance management strategies. This proposal was based on a small number of isolates.…”

“…In Australia, although it appears that the population is largely clonal based on neutral genetic markers, a broad range of aggressiveness exists ( Elliott et al, 2013 ). Hence the Australian chickpea industry is at risk from selective propagation and dispersal of the fittest and best adapted A. rabiei clones.…”

“…Two types of adaptation are recognized in fungal species, generalized adaptation and localized adaptation, both resulting in the production of unique haplotypes with high aggressiveness levels and frequencies, due directly to high survival rates ( Leonard, 1977 ). Elliott et al (2013) first detected clones with differing levels of aggressiveness within the Australian A. rabiei population and proposed that despite its clonal nature, the population contained a large potential to evolve and adapt to overcome chemical and host resistance management strategies. This proposal was based on a small number of isolates.…”