The team established of the pathogenic variability in Ascochyta lentis by establishing a differential set of lentil lines and cultivars. Tests for pathotype variability amongst 219 isolates of A. lentis, sourced from USA, Pakistan, Canada, Syria, China and Australia, revealed that this fungus varied in pathogenicity and 14 different pathotypes were identified. This was greater pathogenic variability than previously observed, and there was geographic separation of some of the isolates. Pathotypes 4 and 10 were only present in Pakistan, pathotype 13 was only present in Syria and pathotype 14 was only present in China. The Australian population of A. lentis appears to be more variable in virulence than those in Canada and Pakistan.
In epidemiological studies, surveys of lentil seed samples produced in Australia showed that A. lentis was widespread in all lentil-growing areas. The most severely infected samples came from the Horsham and Rosebery areas in Victoria. The negative effect of ascochyta blight in lowering seed quality often outweighed the yield losses caused by the disease. Investigations of epidemiological consequences of planting lentil seed with different levels of infection revealed that the frequency of transmission from infected seed to seedling is often low, especially when soil temperature is moderate to high. There was an association between initial seed infection and percentage infection of the harvested seed. However, no correlation was observed between seedling disease and initial seed infection, partly due to extremely low levels of seedling disease.
Although certain cultural practices can reduce the prevalence of ascochyta blight, the use of resistant cultivars has long been recognised as the most practical and effective method in controlling the disease. Therefore, a systematic evaluation of 1705 germplasm accessions from six regions was undertaken at VIDA under glasshouse conditions. The team identified resistance to ascochyta blight, but out of the 1705 accessions only 125 were found resistant.
Wild lentil species closely related to the cultivated form were evaluated as a potential source of resistance to ascochyta blight because of their long period of co-evolution with the fungus. The results were encouraging: for example, among the 32 accessions of Lens nigricans ssp. ervoides, 14 accessions had resistance to ascochyta blight.
The ILL 5588 line has been used extensively as a parent when breeding for resistance to A. lentis. Disease progress studies at Horsham and Rosebery confirmed its field resistance. Tests on harvested seeds also showed a high level of resistance to seed infection. Glasshouse studies on the inheritance of resistance showed that a single dominant gene probably controls the resistance in ILL 5588 to A. lentis.
Crop improvement programs are benefiting from the use of molecular markers to better evaluate their genetic resources. An associated project at the Joint Centre for Crop Improvement (JCCI), Melbourne University, is developing PCR-based RAPD markers to identify ascochyta blight resistance in pulse crops. A preliminary survey, using the same primers to screen lentil accessions identified as being resistant to A. lentis under field conditions, indicates that PCR-based RAPD markers may be useful in future for separating resistant and susceptible lines.
The research confirmed the influence of sowing date on both grain yield and level of seed infection. It was important to establish the ideal sowing times for different cultivars to minimise risk of infection. Fungicidal sprays improved the quality of the seeds produced and also increased yields.