Genotype-Dependent Interaction of Lentil Lines with Ascochyta lentis

Abstract

Ascochyta blight of lentil is a prevalent disease in many lentil producing regions and can cause major yield and grain quality losses. The most environmentally acceptable and economically profitable method of control is to develop varieties with high levels of durable resistance. Genetic studies to date suggest that ascochyta blight resistance genes (R-gene) in lentil lines CDC Robin, ILL 7537, 964a-46, and ILL 1704 are non-allelic. To understand how different R-genes manifest resistance in these genotypes and an accession of Lens ervoides, L-01-827A, with high level of resistance to ascochyta blight, cellular and molecular defense responses were compared after inoculation with the causal pathogen Ascochyta lentis. Pathogenicity testing of the resistant lines to A. lentis inoculation revealed significantly lower disease severity on CDC Robin and ILL 7537 compared to ILL 1704 and 964a-46, and no symptoms of disease were observed on L-01-827A. Histological examinations indicated that cell death triggered by the pathogen might be disrupted as a mechanism of resistance in CDC Robin. In contrast, limiting colonization of epidermal cells by A. lentis is a suggested mechanism of resistance in 964a-46. A time-series comparison of the expressions of hallmark genes in salicylic acid (SA) and jasmonic acid (JA) signal transduction pathways between CDC Robin and 964a-46 was conducted. These partially resistant genotypes differed in the timing and the magnitude of SA and JA signaling pathway activation. The SA signaling pathway was only triggered in 964a-46, whereas the JA pathway was triggered in both partially resistant genotypes CDC Robin and 964a-46. The expression of JA-associated genes was lower in 964a-46 than CDC Robin. These observations corroborate the existence of diverse ascochyta blight resistance mechanisms in lentil genotypes carrying different R-genes.

Evidence of early defence to Ascochyta lentis within the recently identified Lens orientalis resistance source ILWL180

“…These results provide further evidence of the presence of different defence mechanisms among lentil genotypes. In the present work, and as previously reported (Sambasivam et al, 2016, Sari et al, 2017, conidial germination of both isolates was significantly higher on the attached leaflets of the susceptible genotype ILL6002 than on the resistant genotype ILL7537. However, lowest conidial germination percentages were observed on the leaflets of the genotype ILWL180 for both isolates.…”

“…As with previous reports, pre-penetration events were genotype-specific (Sambasivam et al, 2016, Sari et al, 2017 with both isolates exhibiting differential germination percentages, germ tube lengths, as well as timing and percentage of appressoria formation on both the attached and detached leaflets of the three genotypes assessed. These results provide further evidence of the presence of different defence mechanisms among lentil genotypes.…”

“…Similarly, conidia of both isolates produced longer germ tubes and higher appressorial percentages on the detached and intact leaflets of genotype ILL6002 compared to that of genotypes ILL7537 and ILWL180. Further, shorter germ tubes and lower appressoria frequencies were detected on genotype ILWL180 compared to genotype ILL7537, as similarly reported on another Lens ervoides accession L-01-827A (Sari et al, 2017). This is likely due to the timing of activation of structural and biochemical defence responses.…”

“…Successfully germinated conidia develop germ tubes which help the penetration into host tissues by producing an appressorium at their tip (Roundhill et al, 1995). In previous reports, longer germ tubes and higher appressoria frequencies were determined as indicators of host susceptibility to A. lentis (Sambasivam et al, 2016, Sari et al, 2017. Similarly, conidia of both isolates produced longer germ tubes and higher appressorial percentages on the detached and intact leaflets of genotype ILL6002 compared to that of genotypes ILL7537 and ILWL180.…”

Defense responses of lentil (Lens culinaris) genotypes carrying non-allelic ascochyta blight resistance genes to Ascochyta lentis infection

“…Histological differences in the reaction to A . lentis infection and induction of the two major defense signaling pathways employing SA and JA were reported for the lentil genotypes CDC Robin and 964a-46, which carry non-allelic resistance genes for partial resistance to ascochyta blight in comparison with the susceptible check Eston [ 29 ]. This study indicated that cell death inhibition is possibly a mechanism of resistance in CDC Robin, whereas 964a-46 underwent cell death similar to the susceptible control Eston.…”