Onion is one of the most important vegetable crops in the world including Ethiopia. The field experiment was conducted in Arsi zone at Kulumsa Agriculture Research Center and Ziway Dugda districts under irrigation condition. A total of five improved onion varieties were evaluated in Randomized Complete Block Design with three replications with the objectives of studying the performance and adaptability of improved onion varieties for bulb yield and yield related traits in 2017 during off season. The combined Analysis of variance (variety by location) revealed that significant difference between improved onion varieties for maturity date, marketable and unmarketable bulb yield tons per hectare, bulb length in centimeter, and bulb weight in gram was observed. But non-significant difference for plant height in centimeter, total bulb yield tons per hectare and average bulb diameter in centimeter were observed between improved onion varieties. Except variety Adama Red all the tested improved onion varieties (Melkam, Nafis, Nasik Red and Bombay Red) was well performed and adapted. These varieties were gave more than 40 marketable bulb yield t ha -1 . So those improved onion varieties were recommended for the study area and areas of similar agro-ecological zones under off season growing condition.

The aim of the experiment was to determine the correlations between tuber yield and yield components and to measure the direct and indirect effects of yield components on tuber yield of potato genotypes. The experiment was conducted using eleven potato genotypes with one standard check variety (Belete) and a local check at Kulumsa Agricultural Research Center, Bekoji sub-station during 2020-2021. Data were collected for tuber yield, tuber dry matter content (%), plant height (cm), stem number, specific gravity, and phenological parameters. Since the two seasons had heterogeneous error variance, analysis was carried out separately. In 2020, correlation analysis indicated that the tuber yield was positively and significantly associated with stem height (0.608), marketable tuber (0.997) and positively associated with tuber dry matter content, stem number per plant, days to maturity, while it was negatively correlated with specific gravity, days to emergence and days to flowering at the genotypic level. Total tuber yield was positively and significantly correlated with days to maturity (0.640), stem height (0.791), marketable tuber (0.977) and stem number at the genotypic level. While specific gravity was positively and significantly correlated at the phenotypic level; and negatively at the genotypic level in the second season. Results of path analyses indicated that marketable tubers had the highest positive direct effect (+1.059) on total tuber yield followed by days to flowering (+0.057) and specific gravity (+0.026) in 2020 while marketable tuber (0.7107), stem height (0.2842), tuber dry matter content (0.0078), days to maturity (0.1250) had also positive direct effect in 2021. In addition, most of the indirect effects of yield components on tuber yield were significant and positive. Significant effects of marketable tuber, tuber dry matter content, days to maturity and stem height on total tuber yield, indicated that they could be used as the criteria for potato improvement and breeding programs. Int. J. Agril. Res. Innov. Tech. 12(2): 144-154, December 2022

Potato is one of the most important crops in the farming system of Bekoji and Kofele in the cool highlands of Arsi where potato is usually grown biennially during the main and 'bulg' seasons. 'Belete' has been the dominant potato variety in these areas for the last ten years now and farmers prefer to grow this variety for its high productivity and resistance to late blight disease. Nevertheless, farmers have complaints on its big sized tubers, considered as unmarketable, which costs them more seed to cover a given area of land and less suitable for cooking. Besides, farmers often use random population density and time of harvesting, which also contribute to this problem. The present study was therefore intended to manage the tubers' size distribution of this variety without negatively affecting the yield of the crop through modifying plant spacing and time of harvesting from previously recommended practices. Twelve combinations of four plant spacing and three time of harvesting were studied on variety "Belete' at Bekoji and Kofele in the main seasons of 2018 and 2019. The experiment was laid out in a completely randomized block design with 4x3 factorial arrangement in three replications. The analysis of variance revealed that the interaction effect of spacing and time of harvesting significantly (p<0.001) affected the marketable tuber yields. The narrow spacing (60cmx20cm) or high population treatment (83,333 plants/ha) with 120 days after planting resulted in the highest marketable and total tuber yield compared to the rest. While the least yields were recorded from the wider spacing of 75cmx30cm (44,444plants/ha) and early harvesting (90 days). The spacing 60cmx20cm did 17.2% increment in marketable yield over the previously recommended spacing of potato (75cmx30cm, 44,444plants/ha). From this study, therefore, it can be recommended for Belete that the narrow spacing of 60cmx20cm and harvesting at 120 days after planting could be the optimum spacing and time of harvesting to produce marketable tubers.

The experiment was carried out under rain fed conditions for three consecutive years (2017–2019) from mid-June to mid-October at Bekoji and Kofele sub sites of Kulumsa Agricultural Research Center, Ethiopia by using improved varieties to identify superior genotypes. The experiment was laid out in a randomized complete block design with three replications. The results of analysis of variance (ANOVA) showed that the presence of significant (p<0.05) differences among genotypes for all traits studied. Analysis of variance revealed that location by year effect had highly significant difference at (p<0.01) for all traits except specific gravity which showed significant difference at (p<0.05). Treatment by location showed significant difference except stem number plant-1, total yield, and specific gravity. Treatment by year showed significant differences except for days to flowering. The highest marketable tuber yield was obtained from genotype CIP 395037.107 followed by variety Belete and CIP 395015.6 genotype. Simple correlation analysis revealed that total tuber yield showed strongly and positively significant correlation with average stem number plant-1, stem height and marketable yield. Thus, it could be concluded that genotypes, year and location variations as well as their interaction had considerable influence on tuber yield and the potato’s attributes. The significant interaction effects of genotypes, location, year and positive and strong association between total yield and other traits indicates the need to test potato genotypes over season and location in order to select stable and high yielder genotypes.