Effects of Temperature Stresses on the Resistance of Chickpea Genotypes and Aggressiveness of Didymella rabiei Isolates

Chickpea (Cicer arietinum L.) is an important food and rotation crop in many parts of the
world. Cold (freezing and chilling temperatures) and Ascochyta blight (Didymella rabiei)
are the major constraints in chickpea production. The effects of temperature stresses
on chickpea susceptibility and pathogen aggressiveness are not well documented in
the Cicer-Didymella pathosystem. Two experiments were conducted under controlled
conditions using chickpea genotypes and pathogen isolates in 2011 and 2012. In
Experiment 1, four isolates of D. rabiei (AR-01, AR-02, AR-03 and AR-04), six chickpea
genotypes (Ghab-1, Ghab-2, Ghab-3, Ghab-4, Ghab-5 and ICC-12004) and four
temperature regimes (10, 15, 20, and 25◦C) were studied using 10 day-old seedlings.
In Experiment 2, three chickpea genotypes (Ghab-1, Ghab-2, and ICC-12004) were
exposed to 5 and 10 days of chilling temperature exposure at 5◦C and non-exposed
seedlings were used as controls. Seedlings of the three chickpea genotypes were
inoculated with the four pathogen isolates used in Experiment 1. Three disease
parameters (incubation period, latent period and disease severity) were measured to
evaluate treatment effects. In Experiment 1, highly significant interactions between
genotypes and isolates; genotypes and temperature; and isolate and temperature were
observed for incubation and latent periods. Genotype x isolate and temperature x
isolate interactions also significantly affected disease severity. The resistant genotype
ICC-12004 showed long incubation and latent periods and low disease severity at
all temperatures. The highly aggressive isolate AR-04 caused symptoms, produced
pycnidia in short duration as well as high disease severity across temperature regimes,
which indicated it is adapted to a wide range of temperatures. Short incubation and
latent periods and high disease severity were observed on genotypes exposed to chilling
temperature. Our findings showed that the significant interactions of genotypes and
isolates with temperature did not cause changes in the rank orders of the resistance of chickpea genotypes and aggressiveness of pathogen isolates. Moreover, chilling
temperature predisposed chickpea genotypes to D. rabiei infection; developing multiple
stress resistance is thus a pre-requisite for the expansion of winter-sown chickpea in
West Asia and North Africa.