Use of Resistant Varieties of Wheat to Combat Yellow Rust in Himachal Pradesh
Authors: Dr. Madhu Patial and Neha Sharma
Wheat (Triticum aestivum L.) an important food grain for sustenance, accounts for 19 percent of the world total production among major cereal crops. No doubt the tremendous increase in the wheat production has been seen from years, however, a quantitative jump in wheat production and productivity is still needed to feed the fast expanding human population accompanied with the drastic changes in world climatic conditions. There are number of constraints that limit the potential of wheat varieties for further increase in production, one of the most critical and important to consider is the wheat rust disease. Rust is a super spreading fungal disease also known as “polio of the agriculture” which can cause massive crop failure within a few weeks. Wheat rust causes annual average loss of up to 10-20 percent or more when susceptible and very susceptible varieties are grown. According to Park (2007), wheat leaf rust alone can cause up to 60% yield losses while stem rust can cause 100% yield losses in severe conditions. Yellow rust can cause yield losses of up to 100% on susceptible cultivars if infection occurs very early in the crop development stage and the disease continues to develop during the growing season. Recently, stem rust on wheat caused by a new race TTKSK (e.g. isolate Ug99) has been in limelight and was found to spread across Africa, Asia and the Middle East nations. Because of the constantly changing nature and identification of new isolates like Ug99 and Yr27, researchers are now more inclined towards stacking of different types of resistance genes. Rust causes yield losses by removing sugars and nutrients for itself thereby weakening the plant. The varieties grown by the farmers carries some known disease resistance genes against rusts, however, most of the resistance genes are known to be broken down.
In Himachal Pradesh, wheat is the most important cereal crop which is sown throughout the State in the Rabi except in Lahaul & Spiti, Kinnaur, Pangi and Bharmour areas of Chamba district, where it is cultivated in summer (April-May to September-October). The percent share of wheat in H.P toward national share in area is 1.41% and in production is 0.84% with the productivity of 1609 Kg/ha. Of the three rust, yellow rust caused byPuccinia striiformis (PST) Westend. f. sp. Tritici Eriks. is the main dominating one in Himachal Pradesh. Yellow rust takes its name from the appearance of yellow colored stripes which are produced parallel along the venations of the leaf blade. The yellow stripes are the uredinia that produce yellow color uredinospore. This powdery yellow stripe hinders the photosynthesis making plant weak and stunted. The infected plants have fewer spikes, decreased number of grains per spike, shriveled grains and decreased grain weight.
Yellow rust usually occurs early in the growing season, when temperature ranges from 2-150C, but it may occurs to a maximum of 23 0C. Higher humidity and rainfall are the favorable conditions for increasing the infection on both leaf blade and leaf sheath and even on spikes when in epidemic form. The fungus is airborne and spreads through urediospores. Pathogen survives in the cool temperature of hills (Himalayas and Nilgiris) and the primary infection takes place by middle of January in the foot hills and sub mountainous parts of the North Western India. The infection also comes from across the western border and from Nilgiri hills but yellow rust from Nilgiri Hills cannot come out of the zone due to high temperatures in the Peninsular and Central India.
Use of chemicals
While use of chemical fungicides like propiconazole (Tilt 25 EC @ 0.1 per cent) at yellow rust initiation for controlling the disease in wheat exist, but scientists are engaged for the development of more rust resistant wheat varieties to combat the disease.
Use of resistant varieties
The effective fungicides for controlling stripe rust should be used only as support and not as substitute for growing resistant varieties. For farmers of H.P varieties like HS562, HS 542, HS507, VL907, VL892, HP349 etc can be adopted not only as a check for yellow rust but also they have high yielding ability and other desirable traits. Rust pathogens can mutate to overcome the existing resistant genes. Therefore, breeding for rust resistance needs to focus on maintaining current levels of resistance and on developing new and improved sources of resistance. This requires a continuing search for the development and identification of new forms or combinations of resistance, to ensure that the varieties in farmers’ fields have effective genetic resistance against the current strains of the pathogens.
How Plant Breeding can help?
Use of resistant varieties has been pointed out as the most economical management strategy by many workers. A number of rust resistance genes are known that provide complete protection (McIntosh et al., 1995) but due to narrow genetic base of varieties and higher rate of mutation in rust, the wheat cultivars are becoming susceptible to rust disease. Hence, the researchers are continuously deploying wheat yellow rust resistance varieties due to the boom and bust cycle of the pathogen and host. Most of the experts have now called for the diversity in wheat crop with different type of rust resistant genes as the need of the hour. Sources of resistance are available and have been used by the breeders from long time. However, achieving durable resistance is difficult task as the rust disease continues to evolve and circumvent the breeders’ achievements. As Dr Borlaug has highlighted that “rust never sleeps” and it’s continuously changing nature makes breeder work more demanding. Hence, the breeder has to be continuously engaged in rust resistant varietal development programme which is time consuming, but surely with the advancement of different biotechnological tools, we can save lot of time and can plan ahead of new variants of yellow rust.
About Author / Additional Info:
ICAR-IARI, Regional Station, Shimla (H.P)