Abiotic stress effects associated with climate change on yield and tuber quality of potato cultivars in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, School of Agriculture and Environment, Massey University, Manawatu, New Zealand

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The recent weather anomalies in New Zealand, particularly the summer heatwaves of 2017/18 and 2018/19, hottest and third hottest on record, respectively, have seemingly affected potato production. The purpose of this research is to determine how abiotic stress commonly associated with climate change, e.g., drought and heat, is affecting the current potato production in New Zealand, define its effects on yield and tuber quality of commercial potato cultivars, and determine if cultivars exhibit differential susceptibility. Secondary climate data in the past 60 years (1958–2018) during the potato growing months of October to March showed an increasing trend for temperature in Ohakune (+0.53 °C), Opiki (+0.36 °C), and Hastings (+0.28 °C) as well as a decreasing trend for rainfall in Ohakune (-24.8 mm) and Hastings (-48.7 mm). The increase in temperature also increased the number of days with supra-optimal atmospheric temperatures believed to delay (>25 °C) or inhibit (>30 °C) tuber growth in Hastings by 57 days (2017/18 season) and in Opiki by 103 days (2018/19 season). Baseline data from a preliminary study during the 2017/18 growing season showed that abiotic stress associated with the extreme weather conditions apparently affected the yield and tuber quality, with cultivars showing differential susceptibility. Up to 85% unmarketable tubers were recorded among the samples collected, which was attributed to the high incidence of a wide array of tuber physiological disorders. The multi-environment trial in the 2018/19 growing season showed that abiotic stress had significant effects on the different morpho-agronomic and physiological functions of the potato crop and ultimately affected the yield and tuber quality. Abiotic stress increased the incidence of tuber physiological disorders, e.g., tuber malformation, growth cracks, and second growth, which reduced the total yield and marketable yield by up to 43.3% and 45.1%, respectively. Additionally, genotype × environment analysis showed that cultivar ‘Taurus’ is the most stable and adaptable cultivar across trial sites (wide adaptation). At the same time, cultivars ‘Hermes’ and ‘Snowden’ are tolerant to heat and drought stress (Opiki) and heat stress alone (Hastings) (specific adaptation), respectively. The glasshouse and plant growth chamber trial revealed that drought stress (DS) generally reduced the plant height, number of leaves, and canopy cover but enhanced the formation of more but smaller stomata and glandular and non-glandular trichomes. DS also encouraged the closing of the stomatal aperture potentially to reduce water loss, thereby reducing the transpiration rate (E), stomatal conductance (gS), and net photosynthesis (PN), which potentially affected the final yield. Conversely, heat stress (HS) increased the plant height, canopy cover, and number of leaves and developed more and larger stomata. HS also stimulated stomatal opening, leading to enhanced E and gS and improved PN at the vegetative stage. On the other hand, in general, the combination of drought and heat stress exacerbated the adverse effects of each abiotic stress type on the different morpho-physiological parameters. As established in the various component trials of this research, different abiotic stresses associated with climate change have a significant effect on the morpho-agronomic and physiological functions of potato crops and negatively impacts the yield and tuber quality. Breeding of new cultivars, and mass selection of existing cultivars should be conducted through multi-environment trials to identify adaptable cultivars that can be used to mitigate the effects of abiotic stresses associated with climate change on potato crops in the field and to increase the resiliency of the New Zealand potato industry.
Potato industry, New Zealand, Potatoes, Effect of global warming on, Effect of stress on