Rust disease: A new threat to chickpea cultivation in transitional tract of Karnataka
Chickpea (Cicer arietinum L.) is one of the ancient food legume cultivated by humans. It is an extremely important pulse crop in semi-arid areas of central, south and southeast Asia. In India chickpea is the most important pulse crop contributing to over 40% of country’s total pulse production. However the area under this crop has been decreasing in the traditional areas of north and north western India. On the other hand the area under chickpea in central and peninsular India is increasing. Karnataka is a major state in peninsular India with 9.6 lakh ha. area under chickpea cultivation and production of 6 lakh tones. The productivity is very low in this region (629 kg/ha). The main reasons for low productivity are susceptibility of chickpea cultivars to biotic and abiotic stresses which reduces yield and yield stability. Moreover environmental conditions in this region are favourable to the pathogen. More than 50 pathogens have been reported to affect chickpea which includes both soil and air borne pathogens. Most of research efforts were made in developing resistance to soil borne fungal pathogens and the foliar fungal diseases are of least importance, without much yield loss. But in the recent past chickpea rust is becoming major threat to chickpea cultivation, particularly in transitional tract of Karnataka.
Chickpea rust and its importance:
Among the foliar diseases, Chickpea rust is caused by Uromyces ciceri-arietini. It was considered as a minor disease as it appears late in the season when the crop is maturing and hitherto, it was never noticed in epiphytotic scale India, particularly in Peninsular region. Hence, no serious research efforts were made to develop rust resistance varieties in chickpea. The disease is widespread elsewhere-in the Mediterranean, southeast Europe, south Asia, east Africa and Mexico, but is usually considered to be of only local importance. It has been reported as a significant problem affecting chickpea production in central Mexico and Italy. It was reported for the first time in Mexico during 1961, United States in 1985. In both the countries the spread of the disease was very fast and almost all the cultivars were susceptible. In Karnataka the chickpea rust epidemic was reported for the first time during the year 1987. It has not received much attention so far, as it appears late in the season when the crop is maturing. It has caused significant yield losses in chickpea growing transitional tract of Karnataka during rabi 2008-09 and2009-10. The severity of disease is very high causing 80 to 100 percent yield loss. However during rabi 2010-2011, disease was observed in only few areas, where late sowing was done.
The chickpea rust disease first evidenced as small round or oval, light brown to dark brown pustules on both surfaces of foliage. Such lesions appeared in large numbers on lower surface (Fig. 1b). In advanced stages, the sori also seen on upper surface of leaf, pods and occasionally on stem. In majority of the cases the individual sori covered the entire leaflet and measured from 1-5 x 1-3 mm. These sori gave a brick red colour to the infected plants which could be identified from distance.
Morphology of the pathogen:
Uromyces ciceri-arietini is a hemiform, the pycnial and the aecial stages being unknown. The uredia are as a rule hypophyllous and scattered, minute, round, pulverulent, when mature and cinnamon-coloured. The urediospores are globose to subglobose, loosely echinulate, 20 x 28 µ in diameter, yellowish-brown with a rather thick epispore and four to eight germ pores. The telia resemble the uredia but are darker brown; the teliospores are variable in shape, round, ovate or angular with a roundish, unthickened apex and brown, warty or roughened wall. They measured 18 to 30µ by 18 to 24µ and have a short, hyaline pedicel from which the teliospores get readily detached. They have a single germ pore, which fact and their somewhat deeper coloured epispore distinguish them from urediospores.
Viability and germination of uredospore:
Temperature is the key factor for both viability and germination of uredospore. The uredospres remain viable for 48 weeks when stored at 6-70c but are killed within two weeks if exposed 30-350c. Fresh spores can be germinated in tap water at 180c. At this temperature germination commences in 2.5 hours. However, these spores lose their viability and germination even on host plant at temperature above 350c.