The response of growth rate to temperature in seedlings of several Allium crop species

SUMMARY Relative growth rates (R w ), leaf area ratios (LAR), net assimilation rates (NAR), and leaf weight ratios (LWR) were estimated for seedlings of onion, leek, Japanese bunching onion and chives grown at constant temperatures of 10, 12, 15, 19, 23, 27 and 31 d̀C. R w was greatest at 19 d̀C in Japanese bunching onion and chives, and at 27 d̀C in onions and leeks. R w increased approximately linearly between 10 and 19 d̀C in all species; between 19 and 27 d̀C it either increased further, decreased or remained constant depending on species but at 31 d̀C R w was lower than the maximum in all cases. LAR's were greatest at 27 d̀C in onions and leeks and at 23 d̀C in the other two species. Between 10 and 19 d̀C both LAR and NAR increased in all species. Between 19 and 27 d̀C increases in LAR were compensated for by decreases in NAR with the result that R w showed little change with temperature. Averaging over all temperatures the species were ranked in order of decreasing R w , NAR and LWR as onion, leek, Japanese bunching onion and chives. For LAR this ordering was reversed with respect to onions and leeks. Plant to plant variability increased in the order onion, leek, Japanese bunching onion then chives. Although onions were the fastest growing of the Alliums tested their R w was lower than that of several other vegetable species for which R w was similarly measured.