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Impact of episodes of high temperature on physiology, growth and yield performance of potato (Solanum tuberosum L.)

Obiero, Charles Otieno (2018) Impact of episodes of high temperature on physiology, growth and yield performance of potato (Solanum tuberosum L.). PhD thesis, Murdoch University.

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Potato is the most important non-cereal crop for world food security. It is adapted to mild conditions, but its production is rapidly shifting to warmer regions where more and longer episodes of high temperatures are likely to reduce its yield. This will exacerbate the effects of global warming on potato production. Nevertheless, little is understood about how episodes of high temperatures influence potato physiology, growth and tuber yields because most of the research has been conducted under persistent high temperature treatments. This study assessed the potato-growing regions of Western Australia for the actual temperatures experienced by potato plants during the critical period of tuber growth (Chapter 3). It then investigated how the identified episodes of high temperatures influenced leaf growth, photosynthetic rate and dry matter partitioning to the tubers (Chapter 5, 6, 7 and 8). Lastly, it explored whether an agronomic intervention through application of plant growth regulators could overcome the negative impacts of the high temperatures (Chapter 9).

Climate analysis showed the number of hot days above 25 °C increased from 16 to 22 in the various regions in 1985 to 36 to 54 days in 2014. More than seven consecutive days above 25 °C occurred at least once per year in all regions except in Albany. The glasshouse study showed that tuber dry matter was reduced to a similar extent when a 9-day episode of 26 or 30 °C was applied before or after tuber initiation. Even one-day exposure of potato plants to high temperatures subsequently reduced tuber growth. Plants in the high temperature treatments had the same or slightly more tubers per plant than those in the control. More small-sized tubers (tubers with the diameter at the widest part of less than 2.5 cm) were produced when the episode of 30 °C exceeded three consecutive days. There was less starch and sucrose content in the tubers of the high temperature treatments relative to the control, but more sucrose accumulated in the leaves of plants that had been exposed to the high temperature episodes before tuber initiation. The shoot grew at the same rate regardless of the impact of the episode of the high temperatures. After the end of the high temperature period, the high temperature treatments only had 60 % of the leaf area on the main shoot as in the control. The net photosynthetic rate per unit leaf area measured between 12.00 and 2.00 pm during the high temperature period was also reduced more in the older than in the younger leaves. The high temperatures increased the morning (7.00 am to 10.00 am) and the night-time (7.00 pm to 1.00 am) dark respiration rates per unit leaf area regardless of the leaf age. Exogenously applied auxin inhibitor (TIBA) caused similar effects to the high temperature but applying auxin (IAA) did not overcome the negative impact of high temperature on the potato plants.

The reduction in tuber growth in this study is inconsistent with the proposed inactivation of starch synthase (which reduces the conversion of sucrose into starch in the tubers hence reduces tuber growth) or increased production of gibberellic acid (which not only stimulates shoot growth which diverts carbon away from the tubers but also reduces starch synthase activity in potato plants grown at high temperatures). This is because, in the present study, the reduction in tuber growth occurred mostly after the end of the high temperature period when plants were grown back at cooler conditions. Further, the reduction occurred even in plants that had no tubers present at the end of the high temperature period. Moreover, the tubers in the high temperature treatments had less sucrose and starch content rather than the expected increase in sucrose content with inhibition of starch synthase activity. Lastly, the shoot grew at the same rate while the laterals grew more after the end of the high temperature period. In this study, the reduction in tuber growth was more consistent with lower whole plant carbon supply due to reduced leaf area, lower net photosynthesis in older leaves, higher respiration rates regardless of the leaf age and the continued shoot growth. These findings provide new insights into how potato responds to high temperatures.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
United Nations SDGs: Goal 2: Zero Hunger
Supervisor(s): Bell, Richard and Milroy, Stephen
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