Developing cultural and alternative tools to manage Ascochyta Blight in chickpea
Project code: PRR03-200
Yantai Gan - Agriculture and Agri-Food Canada
To optimize cultural and chemical control techniques for the management of Ascochyta blight in chick pea and to provide recommendations for farmers
Summary of Results
Ascochyta blight, a fungal disease caused by Ascochyta rabiei (Pass.) Labrousse (teleomorph, Didymella rabiei (Kovachevski) v. Arx), is the most important constraint to chickpea production in western Canada. Chickpea infected by Ascochyta rabiei produces low seed yield with poor quality, and yield losses in susceptible cultivars can reach 100%. Economic losses due to the disease are substantial in years when late fall is wet. Efforts have been undertaken to breed blight-resistant cultivars, but high levels of the resistance are not yet available in cultivars available to producers. Some cultivars have moderate resistance at the seedling stage, but the resistance declines as plants grow older. Also, the pathogen is genetically diverse, and new pathotypes of the pathogen can appear that render moderately resistant cultivars susceptible. The development of integrated disease management strategies is the key for successful chickpea production.
This project, funded by PMC, led by Dr. Y. Gan at Swift Current, was to determine the effect of cultivars varying in plant architecture and plant population density (PPD) on the severity of ascochyta blight under diverse environments. A total of 12 desi chickpea (with pinnate leaves) and 12 kabuli chickpea (some with pinnate leaves and the others with unifoliate leaves) were studied at 25, 36, 44, 53, and 62 plants m-2 (actual counts 3 wks after initial seedling emergence) at Swift Current from 2002 to 2005 and at Saskatoon in 2004 and 2005.
The results showed that site-years had a significant effect on ascochyta blight epidemics, with the highest severity at Swift Current in 2005 and lowest at Saskatoon in 2004. Across site-years, ascochyta blight was most severe on the cultivar Evans, followed by CDC Xena, and lowest on the genetic line 222B-11. Cultivars with pinnate leaves (or fern leaves) had lower blight severity than those with unifoliate leaves during all growth stages. At the late-pod stage, severity in cultivars with pinnate leaves averaged 15% compared to 48% in unifoliate cultivars. Kabuli cultivars had higher severity than desi cultivars throughout the growing season, and at the late-pod stage, severity was 13% for the desi and 33% for the kabuli.
There was a significant interaction between cultivar and PPD for blight severity. Some cultivars increased the severity of ascochyta blight as plant population increased, whereas the other cultivars had no changes in the severity of ascochyta blight with changes in plant population density. This was due to differences in plant architecture and canopy structure. Plant with more prostrate growth habit tended to increase the disease severity as the plant population density increased, while plants with erect growth habit did not associate the blight severity with plant density. Site-year accounted for the largest portion of the variation in blight severity (69%), followed by cultivar type (25%), and then PPD (6%). Increasing PPD consistently increased seed yield per unit area, despite more disease on the basis of individual plants at higher PPD. Identifying optimum plant populations for groups of cultivars with similar plant architecture should be a component in an integrated strategy to minimize ascochyta blight in chickpea.
Chickpea grown in paired-rows (i.e., two-rows of chickpea plants with 25-cm space alternated with a 75-cm of space between the pairs) was compared with solid seeding (i.e., 25-cm space of uniform seeding) in the 2004 and 2005 field trials. The paired-row seeding patterns reduced fungicide usage and improved coverage of fungicides. As a result, disease infection was significantly less in the paired-rowed chickpea plants compared to solid seeding. Seed yield was equal or greater in paired-rowed chickpea compared to solid seeding. CDC Xena (a large-seeded kabuli type of chickpea) received greater benefits from paired-row seeding than Amit (a small-seeded kabuli chickpea). The large-seeded CDC Xena chickpea bear unifoliate-leaves whereas the small-seeded Amit chickpea have fern leaves. The use of the paired-row seeding patterns in chickpea significantly reduced disease pressure particularly for cultivars with unifoliate leaf type, and therefore potentially reduce the use of fungicides by as much as 30% without sacrifying seed yield.
Knowledge gained from this research is providing producers with improved cultural tools with which producers can manage their chickpea crops effectively and efficiently. The reduced use of fungicides in chickpea reduces the risk to the environment while at the same time yielding healthier and more valuable crops.
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