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The present study was carried out during 2014-15 in the Kullu district of Himachal Pradesh, which is situated between 31º52’00” to 31º58’00” North latitude and 76º13’00” to 77º44’00” East longitudes.The cumulative chill units hours available for apple crop were calculated by using UTAH model for the period of 1986 to 2015 and a decrease of 6.38 chill units(CU) hours per year was recorded at Kullu Valley of Himachal Pradesh. Chill units for the last three decades i.e. 1986-1995, 1996-2005 and 2006-2015 also revealed a decreasing trend of the order of 63.79 CU decreased per decade.Monthly accumulation of chill unit hours during the same period for each winter month (November, December, January and February) revealed maximum decrease of 2.186 CU per year was observed for the month of February. Trend analysis of last five years 2011-2015 showed there was a huge decrease of 14.98 chill units per year. Data on apple productivity in Kullu district for last decade (2005-2014) showed a decreasing trend of the order of 0.183 tons/ha /year as per the regression equation y = -0.183x + 5.745. Thus the climatic conditions for apple cultivation in the Kullu district will be becoming unfavorable in the coming years.

The goal of the present research was to ascertain the potential root endophytic fungi against Dematophora necatrix, Hartig, the causal pathogen of white root rot in apples; however, it has an expanded range of hosts across different fruit trees. Out of 36 endophytic fungi segregated from symptomless roots of apple, wheat, maize, marigold, cherry, and garlic plants, only 9 isolates showed inhibitory effect during preliminary screening and were further assayed under in vitro, pot, and field conditions against the white root rot pathogen/disease. Under in vitro conditions, maximum mycelial inhibition of 81.48% was obtained with the isolate Aspergillus aculeatus strain C2. Microscopic studies on interaction between fungal endophyte with hyphal tips of D. necatrix revealed various morphological abnormalities in the hyphae. In glasshouse conditions, seed treatment pursued by soil application with Crinipellis tabtim strain M8 isolate was highly effective and exhibited 93.55% disease control. Similarly, under field conditions, the overall maximum disease control was exhibited by Crinipellis tabtim strain M8 (84.95%). The most promising root endophytes that were identified rely on morphological and ITS sequence analysis. Root colonization assay was performed which revealed maximum endosphere and rhizosphere colonization with Crinipellis tabtim strain M8. Additionally, confocal microscopic illustrations of transverse sections of root cells tenanted by fungal endophytes as compared to untreated control suggested the persistence and establishment of endophytes in the endosphere of apple seedlings. These findings present the first report on colonization of apple roots by fungal root endophytes suggesting an alternative and sustainable approach for management of white root rot disease.