Photosynthesis and stomatal conductance of five mango cultivars in the seasonally wet–dry tropics of northern Australia

Abstract

Field experiments were conducted over 3 years on 4–6 years old trees of cvs. Kensington Pride (KP), Strawberry (ST), Haden (HA), Irwin (IR) and Tommy Atkins (TA). They belong to two distinct groups, poly-embryonic cultivars (Australia originated KP and ST) and mono-embryonic cultivars (Florida originated HA, IR and TA). There was significant seasonal variation in net photosynthesis rate (Anet) and stomatal conductance (gs) in all the five cultivars with the maximum values observed during the wet season (January–March) and the minimum at the end of June and beginning of July during the dry season. The dry season Anet values showed the largest variation between cultivars in photosynthetic capability. During this season the three monoembryonic cultivars had greater Anet accumulation than the polyembryonic cultivar, KP. Recovery of gs and Anet was marginal and slow after the commencement of irrigation in most of the cultivars following preflowering imposed drought conditions for 2.5 months. The fruit setting and fruit development period was the time of maximum environmental stress, during which gs and Anet remained very low especially for KP in spite of the irrigation and adequate soil water conditions. Significant recovery only occurred in the subsequent wet season when the atmospheric and soil moisture conditions were significantly improved. During the wet season variation between cultivars in Anet and gs was smaller than during the dry season. gs of KP and ST, both polyembryonic cultivars, was often significantly lower than that of monoembryonic cultivars. On both a seasonal and diurnal basis, Anet was highly positively correlated with gs during both the wet and dry seasons. Anet and gs were negatively correlated with leaf-to-air vapour pressure deficit (LAVPD). There was evidence for the poly-embryonic cultivars regulating Anet in response to conditions of high LAVPD to a greater extent than mono-embryonic cultivars in this study. It is concluded that in terms of Anet, cultivars IR and TA were the most suited to a hot tropical environment in contrast to the Australian dominant cultivar KP which did not maintain photosynthesis during periods of environmental stress. This information could be used for breeding programs to improve mango productivity in the Australian tropics.