Inheritance of Seed Set, Germination, and Day Neutrality/Heat Delay Insensitivity of Garden Chrysanthemums (Dendranthema ×grandiflora) under Glasshouse and Field Conditions

Abstract

Commercial chrysanthemums are short day (SD) plants. Recently, several day neutral (DN) garden genotypes have been identified. Both glasshouse and garden cultivars vary in heat delay insensitivity (HDI). This research analyzed yield components (seed set, germination, yield potential) and tested a DN/HDI ideotype for its effectiveness. Progeny from a 6 × 6 diallel were embryo rescued, clonal ramats were grown in two environments (glasshouse—long days; field—long to short days) and evaluated for flowering, early flowering response groups, thermozero temperature response, low long day leaf number (LDLN), high leaf initiation rates, and low mean stem lengths of the terminal shoot. Self seed set ranged from 0% to 8% while outcross seed set was 0% to 92%. General and specific combining ability were highly significant for seed set, the reciprocals, and their interactions. Germination averaged 67%, while yield potential was 44%. Cotyledon pigmentation in embryo rescued seedlings was 7% albinos, 15% anthocyanin (transposable elements), and 78% normal (green). SD parents did not flower in either photoperiod although PPSL-10 carried alleles for DN. SD x DN crosses produced some DN progeny and fit a 1:3 chi square ratio (DN:SD), indicating DN to be recessive. However, DN x DN crosses also fit a 3:1 chi square ratio, due to HDI. No progeny flowered within the 3 to 6 week ideotype; visible bud date had a heritability of h2 = 0.50. Most progeny were within the LDLN range (h2 = 0.72). Several leaf initiation rates exceeded the ideotype (h2 = 0.003); plant height also matched the ideotype (h2 = 0.66). Both visible bud and flowering dates require significant improvement before progeny match the DN/HDI ideotype.