Browsing by Person "Hoelle, Julia"

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Drought affects the synchrony of aboveground and belowground phenology in tropical potato
(2023) Hoelle, Julia; Khan, Awais; Asch, Folkard
The literature describes the belowground and aboveground phenology of potato to be linearly related. Bud formation is synchronous with tuber initiation and flowering with tuber filling. Many agronomic and breeding studies on potato use non‐destructive aboveground phenology to assess belowground development. No information is currently available on the influence of water deficit on the synchrony of above‐ and belowground development in potato. Five contrasting potato genotypes were subjected to four irrigation treatments on two different soil types. The irrigation treatments were as follows: fully watered, early drought, intermediate drought, and late drought. In 5‐day intervals after withholding water, detailed belowground and aboveground development was recorded. Results showed that the synchrony between aboveground and belowground development is strongly influenced by both water deficit and development stage at drought initiation. Under early drought, the aboveground development was hastened and belowground development was delayed. The opposite was found in later development stages. The earlier the drought was initiated, the longer the tuber filling phase was, while the bulking phase was shortened. We concluded that under terminal drought conditions aboveground development and belowground development need to be evaluated separately and cannot follow the standard evaluation system that uses aboveground phenology as a proxy for tuber formation belowground development rates.
Suitability of the stress severity index combined with remote‐sensing data as a tool to evaluate drought resistance traits in potato
(2023) Hoelle, Julia; Asch, Folkard; Khan, Awais; Bonierbale, Merideth
Potato is a drought susceptible crop and even short drought spells reduce tuber yields notably. In an earlier study we developed a stress severity index (SSI) based on the development stage of a genotype at the onset of drought and the soil water deficit based on soil water tension. Here, we test the suitability of the SSI combined with remotely sensed data as a screening tool to select drought‐tolerant potato genotypes. Normalized difference vegetation index (NDVI) and the photochemical reflectance index (PRI) were obtained from reflectance measurements and thermography. Temperature data from the thermography allow using the difference between leaf and air temperature (∆T) to estimate the transpirational cooling of the leaves. Via cluster analysis including SSI, tuber yield reduction under drought, NDVI, PRI and thermography, three groups were distinguished: 1. SSI < 1000 with fast decreasing NDVI, PRI and ∆T, 2. SSI 1000–2000 with almost constant NDVI and ∆T and 3. SSI > 2000 described by small changes of NDVI, PRI and temperature deficit. For SSI < 1000, ∆T, PRI and NDVI showed to be good indicators of genotypic performance under drought. Potential strategies for drought resistance in potato detectable through remote sensing are discussed.