Towards Phenotyping Heat Tolerance in Garden Roses
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abstract
In a world of high throughput genotyping, accurate phenotyping has become a limiting factor to breeding progress. An experiment was conducted to determine which stage of flower development was most susceptible to high temperatures for three garden rose cultivars. Rooted liners of Rosa hybrida 'Belinda's Dream', 'RaDrazz' and 'Sea Foam' were planted in 8.5 cm2 pots in a peat:perlite media and grown in a greenhouse. Well established plants were pruned to leave several nodes with leaves on 2 or 3 main shoots and treatments commenced. The experiment was conducted in two growth chambers held at either 24/17C (optimum) or 36/28C (heat stress) day/night temperatures with 70% relative humidity for eight weeks. Six time and duration heat treatment combinations included eight weeks of continuous optimal temperature, eight weeks of continuous stress, and four sequential two week heat shock treatments including weeks 1-2, weeks 3-4, weeks 5-6 or weeks 7-8. Data were collected on the first flowering shoot of each plant. Days to flower was decreased with continuous heat. The number of nodes to the first flower was not affected by the timing of heat shock treatment, but differed between cultivars. For all cultivars, flower abortion increased with heat applied during weeks 5-6 and weeks 7-8 which corresponded to the time when the flower buds became macroscopically visible. 'Belinda's Dream' had the highest occurrence of flower abortion and 'RaDrazz' had the least flower abortion during this time. Flower size produced under continuous heat was between 30-40% the size of flowers under continuous optimal conditions. 'RaDrazz' had fewer but larger stomata on the abaxial leaf surface compared to 'Sea Foam' and 'Belinda's Dream'.
