Pathogenic variation and virulence related responses of Ascochyta lentis on lentil

Abstract

Ascochyta blight of lentil (Lens culinaris ssp. culinaris) is caused by Ascochyta lentis. The disease causes severe damage to all aerial parts of the plant and may lead to total crop loss during extremely severe epidemics. To identify qualitative differences in resistance within Australian lentil crops, variation in virulence was examined among 17 isolates of A. lentis on six differential lentil genotypes (ILL7537, ILL5588 (cv. Northfield), ILL6002, ILL5722 (cv. Digger), ILL481 (cv. Indianhead) and CIPA203 (cv.Nipper)). Six distinct virulence patterns were identified, with Pathotype I (AL4) being highly virulent, causing disease on all genotypes except ILL7537 and pathotype VI (Kewell) exhibiting low virulence on all genotypes. Histopathology studies were carried out to further understand interaction differences between isolate-host combinations and add to the knowledge of possible resistance mechanisms underlying lentil's defence to the pathogen. The infection process was compared between lentil genotypes with different levels of resistance and isolates with different levels of virulence. Microscopic and biochemical differences were observed between compatible and incompatible interactions, which were related to timeafter-inoculation, with slower responses noted in susceptible lentil genotypes. Relatively fast release of reactive oxygen species (ROS) and a subsequent hypersensitive response (HR) was central to initial defence at the point of penetration in the most resistant lentil genotypes.

Evidence of recent increased pathogenicity within the AustralianAscochyta rabieipopulation

“…It appeared that once the infection structure determined a suitable penetration site, the release of cell wall degrading enzymes and/or secretion of toxins was triggered. Similar findings were observed by Sambasivam et al (2017) and Dadu et al (2018), who identified earlier and stronger H2O2 accumulation in a resistant genotype compared to in a moderately resistant and susceptible genotype in the lentil/A. lentis pathosystem.…”

“…One leaflet from each of four replicates of each host x isolate interaction was inoculated and incubated as described by Sambasivam et al (2017). Briefly, the leaves from each plant were placed with the abaxial surfaces facing upward in a separate petri dish lined with moist filter paper to provide high relative humidity.…”

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

“…Inoculum was prepared as described in Sambasivam et al (2017) and the mini-dome technique of Chen et al (2005) was used to initiate disease. The disease severity of each isolate on each of the host genotypes was assessed using the qualitative 1–9 scale of Singh et al (1981) at 21 days after inoculation (dai) where; scores of 1 or 3 represented a low disease severity; 5 represented a moderate disease severity without significant stem infection, and 7 or 9 represented a high disease severity with stem lesions that would lead to major difficulties in transpiration, photosynthesis and/or breakage.…”

A Novel Lens orientalis Resistance Source to the Recently Evolved Highly Aggressive Australian Ascochyta lentis Isolates

“…Several of these were found susceptible or moderately susceptible to recently detected highly aggressive Australian isolates, with predicted increasing industry reliance on those that remained somewhat resistant, such as PBA Jumbo2 and PBA Harricane XT (Davidson et al, 2016). This will again likely lead to increased selection pressure on the highly variable pathogen population (Nasir and Bretag, 1997b, 1998; Davidson et al, 2016; Sambasivam et al, 2017), to evolve and overcome the relatively few resistance sources upon which the industry is currently reliant.…”