Identification of heat-tolerant chrysanthemum [Dendranthema ×grandifolia (Ramat.) Kitamura] genotypes for commercial production in hot areas of the world is desirable. The extent to which electrolyte leakage from chrysanthemum leaf discs, measured using a test for cell membrane thermostability (CMT), could be related to the delay in flowering induced by heat in the field-grown plants was determined. The relationship between the relative injury (RI) occurring in leaf tissue discs of chrysanthemum cultivars and treatment temperature was sigmoidal. A single temperature treatment at 50 °C resulted in injury values near the midpoint of the sigmoidal response curve and showed the greatest sensitivity in detecting genotypic differences in heat tolerance. The cultivars with a low RI value are those with the greater CMT and shorter heat-induced delay to flowering.
Lilium longiflorum Thunb. cv. Nellie White bulbs were shipped in 1969, 1970, and 1971 from the west coast to St. Paul by air freight from July to October at 15 day intervals. Bulbs were given 0 or 2 weeks of 10°C, 15.5°C or 21 °C followed by 0 or 6 weeks of 4.5°C. Two weeks exposure to 10°C enhanced shoot emergence and flowering of late-harvested non-cooled bulbs and enhanced flowering of cooled bulbs. Treatments of 15.5°C or 21°C had little influence on shoot emergence and flowering of non-cooled bulbs and delayed flowering of early harvested cooled bulbs. With time and with increased bulb growth the degree of dormancy (delay of emergence) decreased and degree of maturity (enhancement of early flowering by 4.5°) increased.
Dormancy of non-cooled Lilium longiflorum Thunb. cv. Ace bulbs was broken with GA3 (1000 ppm), while ABA (500 ppm) partially negated the effect of vernalization on dormancy breaking. Infusion of bulbs with GA3 or ABA had little effect on days to anthesis. Injections of GA3, GA4, or GA7 into shoots from non-cooled bulbs did not substitute for vernalization or affect days to anthesis. ABA injections into shoots from cooled bulbs partially negated the effect of vernalization and delayed anthesis. Injections of GA3 or GA7 into shoots from cooled bulbs decreased days to anthesis, while GA3, GA4 or GA7 increased plant height. ABA delayed anthesis and reduced stem elongation. The major effect of exogenous GA applications appears to stimulate bolting.
Lilium longiflorum Thunb. cv. Nellie White shoots rapidly emerged and flowered when bulbs were given a 4.5°C/40 day treatment. However, GA levels in the bulbs did not increase during the 4.5°C/40 day cold storage, but increased afterwards in the greenhouse with a GA maximum 30 days past storage. ABA activity patterns were similar to GA. Bulbs first treated at 4.5°C/30 days and then followed by 21°C/30 days had higher GA activity and their shoots were slower to emerge and flower than those of bulbs first treated at 21°C/30 days then given 4.5°C/30 days. Bulbs from 4 harvest dates had greater GA activity in the inner scales while ABA activity was greater in the outer scales.