ABSTRACT
Zebra chip disease (ZC) is caused by the fastidious, phloem-limited, bacterial pathogen ' Candidatus Liberibacter solanacearum (Lso), which is transmitted from plant to plant by the potato psyllid (Bactericera cockerelli (Sulc)). Understanding how ZC impacts potato (Solanum tuberosum L.) physiology, could help growers in making more informed crop management decisions. Measurements of instantaneous leaf physiological responses, such as photosynthetic CO 2 uptake and transpiration on the leaf surface, can be used not only for fast screening of affected plants in the field but also for optimizing irrigation management. Over the 2019 and 2020 field seasons, we characterized time-course photosynthetic physiological responses of potato plants infested by potato psyllids (B. cockerelli (Sulc)) carrying the Lso haplotypes A+B. Potato plants were subjected to different variable-rate irrigation (VRI) treatments (100%, 80%, and 60% of field capacity of the soil) through a center-pivot sprinkler system to examine the impact of the disease on key physiological parameters of photosynthesis and transpiration. Leaf and air temperatures, and hyperspectral profiles of the canopy were also measured and compared. The measurements were made during midday weekly from 25 to 50 days after plant infestation (DAI) with bacteriliferous psyllids. The results showed that many of the measured variables, including stomatal conductance, photosynthesis rate, transpiration rate, quantum yields, and normalized difference in vegetation index started to decrease beginning approximately 28–35 DAI, gradually worsening until 50 DAI, in both 2019 and 2020, as the infection proceeded. The decreases in stomatal conductance in infected plants led to decreases in photosynthesis and transpiration. In turn, reduced transpiration resulted in increased leaf temperature due to decrease in evaporative cooling on the leaf surface. Higher leaf temperatures under hot and dry conditions with high light intensity during the daytime would further reduce photosynthetic light harvesting, which is supported by our data, indicating the damage to the photosynthetic pigment formation and machinery. These findings support the previous report that increased leaf temperature in infected plants may have been derived from the closure of stomata in hypersensitive reactions to infection. These stomatal responses were detected within 28 DAI, a week earlier than the differences in hyperspectral profiles observed 35 DAI, and could be implemented in early disease detection strategiesusing measurements of leaf temperature. • Stomata in zebra chip (ZC) diseased potatoes closed and did not recover over time. • Closed stomata caused leaf temperature to increase, damaging ZC diseased potatoes. • ZC disease symptoms can be differentiated from those under water deficit. [ FROM AUTHOR] Copyright of Agricultural Water Management is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)
ABSTRACT
While many studies on zebra chip (ZC) disease in potatoes have focused on the epidemiology of the disease and the characterization of infected potato plants, this study quantifies the impact of ZC disease on crop response and investigates the relationship between irrigation level and ZC disease severity. In this two-year study chipping potatoes were planted under a variable rate irrigation center pivot sprinkler using a split-plot design with a 2 × 3 factorial combination of ZC disease level (diseased and non-diseased) and irrigation levels of 100%, 80% and 60% replenishment of soil water depletion to field capacity, designated I 100 , I 80 and I 60. Crop response of tuber yield, evapotranspiration (ET c), crop water productivity (CWP) and irrigation water productivity (IWP) from ZC diseased plots were compared with non-diseased (control) plots. Tuber yield and CWP in the infested plots were significantly reduced by at least 58% in 2018 and by 21% in 2019 as compared with results in the control plots. Year significantly affected crop response in the control plots, however, crop response in the ZC diseased plots was devastative to potatoes from year to year. There was no interaction between irrigation level and ZC disease occurrence. In both years, stomatal conductance measurements in ZC diseased plants were reduced 35 and 44 days after infection as compared with control plants. Since irrigation did not lessen the severity of ZC disease, as soon as diseased plants are identified within a field, withholding irrigation to the affected areas could improve IWP at the field level. Future studies should consider the use of thermal imaging or spectral reflectance of the plant canopy for spatiotemporal detection of ZC disease as early as possible in the growing season. • Zebra chip disease reduced fresh tuber yield by at least 58% in 2018 and by 21% in 2019. • Stomatal conductance and the ability to uptake water were limited in ZC diseased potato plants. • The interaction between Zebra chip disease and irrigation level was not significant. [ FROM AUTHOR] Copyright of Agricultural Water Management is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full . (Copyright applies to all s.)