Associations between heat tolerance, water consumption, and morphological characters in Chinese cabbage

Variations with regard to heat tolerance, in terms of heading ability, and water consumption under high temperatures were studied in various Chinese cabbage (Brassica campestris spp. pekinensis Rupr.) varieties. Total water consumption did not differ among entries; however, heat tolerant varieties had greater water uptake than heat sensitive ones at the onset of head formation. Heat tolerant varieties also possessed thicker leaves, higher leaf sap electrical conductivity and chlorophyll content, and lower stomatal number. These characteristics appeared to facilitate water transport to the leaves and reduce transpiration, thus enabling the heat tolerant plants to maintain leaf turgidity during the heading stage at high temperature. Vigorous root growth also seems essential to supply adequate water to the leaves so that they can maintain good turgor at high temperature. Breeding for heat tolerance in Chinese cabbage may be accomplished indirectly by selecting for plants which possess relative thick leaves, high levels of electrolytes, high chlorophyll content, few stomata, and vigorous root growth.