Using hydroponics and novel non-destructive pot culture systems which enable inoculation at specific tuber development stages, the dynamics of common scab infection patterns in potato were studied in order to provide more precise identification of tuber physiological factors associated with susceptibility. At the whole-tuber level, infection percentages were greatest when Streptomyces scabiei inoculation occurred early; at 2 weeks after tuberization (WAT) 68% of tubers became infected, contrasting with late inoculation (8 WAT), when only 4% infection occurred. The first-formed internodes were most susceptible to infection, whilst later-forming and slower-expanding internodes were less susceptible. Detailed tuber physiological examination of internode 2 showed that pathogen-induced changes, including increased phellem (periderm) thickness, cell layers and phellem suberization (key physiological features believed critical to S. scabiei infection) were promoted through S. scabiei inoculation. Sequential harvesting showed enhanced phellem suberization (28% greater than the control) within 7 days of pathogen exposure, while phellem thickness and layer responses were also initiated early in the infection process (10-14 days after pathogen exposure) and these responses were independent of symptom expression. Differences in cultivar response were observed, with greater phellem suberization observed 10 days after tuberization (DAT) in the common-scabtolerant cv. Russet Burbank than in the susceptible cv. Desiree. Likewise, Russet Burbank had thicker and more numerous cell layers in the phellem (up to eight cell layers) during early tuber growth (20-30 DAT) than Desiree (up to six cell layers).

Fungicide application is an effective management option to control late blight of potato (caused by Phytophthora infestans). Field experiments were conducted to evaluate the efficacy of recently introduced and previously used fungicides on late blight management and potato yields in the western plains of Nepal in 2015 and 2016 crop seasons. Fungicides and a non-treated control (NTC) were replicated three times in a randomized block design planted with late blight susceptible cultivar Cardinal. Chlorothalonil, copper oxychloride, dimethomorph, fenamidone + mancozeb, mancozeb and metalaxyl were sprayed in 2015. In 2016, carbendazim was used instead of chlorothalonil. The area under disease progress curve (AUDPC) was consistently reduced in years by dimethomorph (90% and 65% in 2015 and 2016, respectively), fenamidone + mancozeb (68% and 62%) and mancozeb (40% and 47%) compared with the NTC. Similarly, tuber yield was increased with the application of dimethomorph (266% and 146% in 2015 and 2016, respectively), fenamidone + mancozeb (211% and 155%) and mancozeb (136% and 116%) compared with the NTC. Chlorothalonil reduced AUDPC by 43% and increased tuber yield by 170% in 2015. Other fungicides either had inconsistent results or did not reduce late blight severity and consequent effects on potato yield. The overall benefit-cost ratio was highest for dimethomorph in both years. These results show efficacy of dimethomorph, fenamidone + mancozeb and mancozeb in reducing late blight severity and increasing potato tuber yield in the plains of Nepal. K E Y W O R D S disease management, foliar fungicide, late blight, potato

Plastic house technology and arrival of hybrid varieties have increased the possibility of tomato cultivation in rainy season in high hills. An experiment was conducted to assess the performance of tomato varieties under plastic house for two consecutive years from 2009 to 2010 at National Commercial Agriculture Research Program (NCARP), Pakhribas (1750m), Nepal. The experiment consisted of eight tomato varieties namely, All Rounder, Bishesh, Dalila, Manisha, Srijna, Suraksha, Trishul and US-04 laid out in a randomized complete block design with three replications. The varieties differed significantly for all observed traits. The highest marketable yield was recorded from All Rounder (86.6 t ha-1) followed by Srijana (80.8 t ha-1). Srijana took the shortest period for flowering and harvesting with an average of 37 and 77 days after transplanting respectively. This was also the tallest variety (268.7 cm) with more clusters (36.23) per plant. However, the highest average single fruit weight was recorded from Manisha (61.94g), and the largest fruit size in US-04 with a diameter of 5.78 cm. Based on yield parameter, the varieties All Rounder and Srijana are recommended for commercial cultivation under plastic house conditions.DOI: http://dx.doi.org/10.3126/njst.v12i0.6473 Nepal Journal of Science and Technology 12 (2011) 17-22

This experiment was conducted to assess the genotypic variation for the growth, yield and yield components of potato grown under drought and irrigated conditions at Hattiban Research Farm, Khumaltar during the summer cropping season (Feb.-May) of the two consecutive years (2013 and 2014). The results revealed that canopy cover, stem height and number of leavers were more sensitive to drought and the effect was more pronounced in early cultivar Desiree. Stem height and leaf number of plant were more (36% and 45%, respectively) reduced in Desiree than other genotypes. Mean tuber number decreased by 55% under drought condition. Drought stress reduced marketable tuber number by 79% as compared to irrigated treatment. Drought stress reduced the marketable tuber yield from 70% to 87%. The clones CIP 392242.25 and LBr-40 had relatively lower yield loss, and less drought susceptibility index under drought indicating their tolerance to drought in field condition. Further experiment is recommended to study the physiological parameters of these genotypes under different water and soil conditions. Int J Appl Sci Biotechnol, Vol 3(3): 513-519