Potato is considered ‘The King’ in food staples and hardly any domestic kitchen is available which does not use it in one or the other form as it possesses all the attributes to be a potential food crop. Potato is the only non cereal food crop to commend such a high position in the world since being nutritious it can solve the problem of malnutrition and under nutrition if adopted as a major food crop. It has been recognized as a wholesome food and richest source of energy in most countries of the world where it forms important part of the human diet. Potato contains significant levels of phenolic compounds and vitamin C as potent antioxidants (Brown, 2005), which inactivate reactive oxygen species, reduce oxidative damage, lead to improved immune functions and reduce risk of cardiovascular diseases, cancer, cataract, diabetes and aging (Kour et al., 2004). It is one of the efficient source of starch producing plants and yield more carbohydrates per unit area and time, is rich in protein, minerals, vitamins and high quality dietary fibre. Potato protein is superior to that of the cereals being rich in “lysine”, an essential amino acid. Potatoes are also used as feed for livestock and in the industry for the manufacture of starch and alcohol.

Potato is highly remunerative and nutritive crop in Jammu and Kashmir particularly in high altitude cold and cold arid areas of J&K. where it serves as a staple food. An overall production scenario of potato in Jammu and Kashmir depicts that area; production and productivity have sharply increased in past decade (Anonymous, 2006). Its cultivation is carried both in the large tracts as well as in the home gardens. The climatic conditions under which potatoes are grown in Kashmir are similar to those in Europe and North America, but due to lack of suitable high yielding varieties the productivity is far below than that of some of the leading potato growing states in the country. Further the climatic conditions/topography of the valley is congenial for True Potato Seed (TPS) production and potato seed tuber production. Although it is being grown in Kashmir for many years but only few varieties are in cultivation which are either poor yielders, low in quality/and or susceptible to various pests and diseases.

The intensive and extensive cultivation under the most favourable environmental conditions for potato crop production in the state failed to provide significant strides in potato yields, because of a number of production constraints, of which frequent occurrence of may fungal diseases viz., Early blight (Alternaria solani), Late blight (Phytophthora infestans), Powdery scab (Spongospora subterranean), Wart (Synchytrium endobioticum), Leaf black (Cercospora concors), Fusarium Wilt (Fusarium solani f. sp. radicicola), Black scurf (Rhizoctonia solani) and Charcoal rot (Macrophomina phaseolina) are noteworthy and have been taking heavy toll of the produce.

Early blight of potato is one of the most important foliar diseases of potato worldwide (Christ, 1990; Pelletier and Fry, 1990; Shtienberg et al., 1990; Vander Walls et al., 2001). In recent years, increase in A. solani disease on potato foliage has been reported in various potato growing areas (Vloutoglou and Kalogerakis, 2000). Primary damage by early blight is attributed to premature defoliation of the potato plants, resulting in tuber yield reduction. Yield loss estimates resulting from foliar damage incited by early blight on potato vary by location, cropping season, cultivar, and the stage of potato maturity. In general, yield reductions of 5-40 per cent have been reported in Israel (Rotem and Feldman, 1965) and 20-30% in the USA (Christ and Maczuga, 1989; Shtienberg et al., 1990). Early blight may also cause dry rot of tubers, reducing both the quantity and quality of marketable tubers (Folsom and Bonde, 1925; O’Brien and Rich, 1976; Nnodu et al., 1982). Environmental factors such as temperature, wetness duration and relative humidity (moisture) affect the development of early blight on potatoes (Adams and Stevenson, 1990; Harrison et al., 1965; Vloutoglou and Kalogerakis, 2000). Temperature increases A. solani infection and sporulation (Vloutoglou and Kalogerakis, 2000). Water in the form of high relative humidity, rainfall or dew accumulation can increase conidia germination and pathogen infection (Rotem, 2004). Alternating low and high humidity conditions have also been shown to favour disease development (Vander Walls et al., 2001). Early blight is also enhanced through continuous potato production (Olanya et al., 2009). The young plants of potato show high resistance to early blight due to A. solani as compared to older ones (Bambawale, 1978). Within the same plant, the lower leaves which are physiologically different from middle and top ones (Dowley et al., 1975) are more susceptible to certain pathogens with resistance increasing in an acropetal direction. Potato early blight symptoms first occur on the lower senescing leaves, which become chloratic and abscise prematurely.

Under Kashmir conditions, early blight of potato caused by Alternaria solani is posing a great threat for its cultivation. The systemic study on potato early blight has not been conducted so far under Kashmir conditions. Therefore keeping in view the devastating nature of disease a detailed investigation was undertaken to study the role of meteorological parameters on disease development.

1. Materials and methods
The role of various meteorological factors on disease intensity and infection rate (unit/day) on early blight of potato was assessed during the year 2009 and 2010 at Shalimar campus. The weather variables were temperature, relative humidity and precipitation. The field experiment was conducted in randomized block design with five replications. The plants were kept unsprayed to record the disease development under natural epiphytotic conditions. Development of the disease in terms of intensity was recorded periodically at seven day intervals starting from the first appearance of the disease. Disease intensity was recorded on 100 leaves randomly selected from each replication and using 0-5 rating scale. Weekly means of temperature, relative humidity and precipitation that prevailed during each disease scoring date were recorded and correlated with disease development. Coefficients of simple correlation and multiple regression was calculated to determine the effect of weather factors on disease development. Growth of disease development in terms of apparent infection rate (unit/day) was calculated as per formulae of Vanderplank (1963).

Perusal of data revealed that the disease appeared during the second week of May in both the years and become conspicuous during the month of July. The disease intensity reached its peak in the second week of August, beyond which disease severity could not be assessed, because of defoliation. Maximum apparent infection rate of 0.155 (unit/day) and 0.165 (unit/day)   was observed during second week of June in both the years i.e. 2009 and 2010, respectively. The temperature 26.47 and 27.32℃, relative humidity 92 and 91 per cent and precipitation 8.68 and 6.42 mm during 2009 and 2010, respectively, apparently favoured the maximum disease development during these periods.

Table 1 Influence of weather factors on development of early blight of potato during the year 2009

Table 2 Influence of weather factors on development of early blight of potato during the year 2010