A series of experiments were conducted to determine different factors affecting the bulb and seed production of promising cultivars of onions, This dissertation consists of two parts, Part-I envisages the screening of local onion cultivars for bulb production and effect of various factors including plant population, time of sowing, fertilizer application, weeds management practices and field curing treatments, Part-II encompasses the evaluation of cultivars for seed production and different factors affecting seed production, The first three chapters deal with introduc;tion, literature review and general methodology used in various experiments, Chapter 4 and 10 give information about different characteristics of ten cultivars collected from different localities and deal with screening for bulb and seed production respectively, On the basis of promising yield and yield contributing parameters, five cultivars namely Naurang local, Panyalla local, Phulkara, Shah Alam local and Swat-I were selected for further studies, The longest and maximum number of leaves were recorded in cv, Shah Alam local followed by Naurang local and Panyalla local. The highest bulbs survival percentage, bulb diameter and bulb weight as well as maximum bulb yield were found in cv Naurang local succeeded by Shah Alam local, Panyalla local and Swat-I. The cv, Naurang local was earliest in bulb sprouting and flowering, contained greatest number of shoots and leaves, possessed maximum number of flowers umber'', flower diameter and gave maximum seed yield, It was followed by cvs, Shah Alam local, Panyalla local and Swat-I. XXVII The optimum time of planting plays an important role in cultivars performance and obtaining maximum as well profitable yields, Chapter-5 pertains to the effect of different planting dates and transplanting seedlings of different age on the bulb yield and yield contributing parameters of onion cultivars, The planting dates include 271ll October. 111ll November, 271ll November. 111ll December and 2SIll December. The transplanting was done on 121ll January, which corresponded to 11 weeks, 8.714; 6.428; 4.571 and 2.428 weeks old seedlings, The earty planting viz. 27!h October took least time for germination and its seedlings contained longest and maximum number of leaves, The transplanting of oldest seedlings viz. earty sown (27!h October) produced maximum bulb diameter, bulb weight, bulb survival percentage and highest bulb yield, The yield and yield contributing traits decreased progressively with delay in planting or decrease in age of seedlings. Optimum plant density contributes significanlly towards yields. The effect of planting densities on the onion bulb yields and yields related characteristics are discussed in Chapter-So Three planting densities viz. 20. 30 and 40 plants m·2 were tested. The thinly populated plants (20 plants m") contained longesl and maximum number of leaves, greater bulb diameter and bulb weight However. Ihe highest bulb yields were achieved with 30 plants m''z density followed by 20 and 40 plants m''z. The fertilizer application is one of the most i!11portant factors for obtaining high and sustained productivity. Chapter-7 relates to the influence of different doses of NPK application on bulbs production. Different levels of NPK significantly affected Ihe number of leaves plant", leaf length, bulb diameter & weight, bulb survival percentage and bulb yield, The higher of NPK Le. 200-150-100 and 200-150-150 kg ha" enhanced the number of leaves, length of leaves, bulb diameter and weight. number of thick neck bulbs and produced the maximum bulb yields. Weeds lake a heavy toll. The efficacy of different weed management practices is discussed in Chapter-B, Weeds control measures including weedy check, one hand weeding, three hand weeding. application of Pendimathalin 330EC @ 3.125 liters ha" and S-Metolachlor 960EC @ 2.5 liter ha" were used for weeds control and their on bulb yield, Three hand weedings proved superior in controlling weeds density. reducing biomass yield, enhancing all growth parameters and boosting bulb yield. It was xxviii followed by Pendimathalin 330EC @ liter ha·l . liters ha·1 and S-Metolachlor 960EC @ 2,5 Chapter-9 is exclusively devoled to post-harvest techniques viz, field curing of bulbs for different periods (5, 10, and 20 days) and the effect of root burning on re-growth, The data on loss of bulb''s weight of different cultivars 30,60. 90 and 120 days of storage indicated that maximum loss in weight of bulbs was recorded in cv. Phulkara while minimum loss was found in cvs, Shah Alam local and Naurang local, Five days field curing resulted in less loss in number of bulbs, bulbs lost much weight as compared to small and medium bulbs, The sprouting bulbs after 90 and 120 days of storage revealed that maximum sprouting occurred in cv. Swat-I followed by Phulkara while minimum sprouting was noticed in CIIS. Shah Alam local and Naurang local. Large size bulbs sprouted the most succeeded by smalt and medium size bulbs, The least sprouting occurred in 5 days field cured bulbs, The burning of roots did not show any significant effect of roots re-growth, No roots re-growth was observed in 5, 10 and 15 days field cured bulbs after 90 and 120 days of storage, However, it occurred in 120 days field cured bulbs, The application of different rates of NPK on yield and yield contributing parameters has been discussed in Chapter-11. Highest rate of NPK (200- 151}.100 kg ha") delayed sprouting and flowering, HO)Never, it encouraged the number of shoots, length and number of leaves, increased number of flowers umber\ umbel diameter and yield, Chapter-12 deals with the effect of bulb sizes small em), medium (3.5-4.5 em) and large «4.5 em) on bUlb sprouting, morphological and reproductive growth parameters and seed production of different culUvsrs of onion. The bulb sizes differed significantly with regard to number of shoots planr''. Large bulbs contained the maximum number of shoots. The plants developed from large size bulbs possessed the maximum number of umbel planrl , longest flower stalks, highest number of flowers umber1 and maximum seed yield.