Phenology-Adjusted Stress Severity Index to Assess Genotypic Responses to Terminal Drought in Field Grown Potato

Abstract

Potato is a drought susceptible, often rain-fed crop suffering strongly from even short periods of soil water deficit. With global environmental conditions changing, potato clones resistant to variable water supply are needed and identifying them is a major task. Many indices assessing potato tolerance to water deficit have been proposed, albeit none of them takes into account the severity of the stress or the sensitivity of the developmental stage during which the stress occurs. As a result, data obtained on genotypes in one location or season are normally not useful in another location or in a different season. We have developed an index evaluating yield response of potato to water deficit based on the soil tension the genotype was subjected to for the duration of the stress modified by the development stage of the genotype. The sum of the daily values was combined in a stress severity index (SSI). In total thirteen genotypes differing in duration and sensitivity to drought were subjected to four levels of deficit irrigation on two soil types at different development stages over two years. Early drought (early tuber filling) reduced yields up to 95% whereas late drought (late tuber bulking) reduced yields significantly less. SSI depended on the genotypic phenological development and on the soil tension values and ranges between 25 and 3500. The index differentiated genotypic responses well across treatments and soil types, even with these relatively advanced development stages, up to a value of 1000. Beyond 1000, yields were generally reduced by more than 60% and a differentiation between genotypes was not possible anymore. SSI constitutes a method that renders site, location, year, season, and soil type effects comparable for responses of potato clones to soil water deficit. Combining this measure of stress severity with other proposed indices may improve upon their current weaknesses in finding or identifying the underlying traits of drought tolerance in potato.

Drought affects the synchrony of aboveground and belowground phenology in tropical potato

“…Withholding irrigation in staggered intervals resulted in different drought severities, which in turn affected genotypic phenology differently, resulting in competition for assimilates between foliage and tubers (Ivins & Bremner, 1965). In general, drought hastened aboveground phenology and delayed belowground phenology, which resulted in significant genotypic differences in stress intensity during specific growth stages (Hoelle et al., 2020).…”

“…For example, severe water deficit during tuber filling hastened aboveground senescence, which resulted in severe yield reductions (Kuppinger et al., 2014). On the other hand, drought during tuber bulking resulted in longer bulking periods under drought and increased yields (Hoelle et al., 2020).…”

Suitability of the stress severity index combined with remote‐sensing data as a tool to evaluate drought resistance traits in potato

“…A number of yield‐derived drought resistance indexes have been formulated and tested in different environments (Fischer & Maurer, 1978; Moosavi et al, 2008); however, studies allowing to evaluate plant responses to soil water deficit across phenological stages and growing environments are scarce (Hill et al, 2021; Hoelle et al, 2020). Some studies report the phenological stages at treatment initiation, but very few additionally include soil borne stress intensity in the same study (Chang et al, 2018; Deblonde & Ledent, 2001).…”

“…Some studies report the phenological stages at treatment initiation, but very few additionally include soil borne stress intensity in the same study (Chang et al, 2018; Deblonde & Ledent, 2001). The SSI (Hoelle et al, 2020) normalizes stress responses across genotypes, soil type and phenological stages. In the present study, NDVI, PRI and ∆ T decreased rapidly at SSI <1000 and a moderately severe increase in yield reductions (Figure 4), which supports the findings of Gerhards et al (2016) for mild early stress conditions.…”

“…In all studies mentioned above, the drought period was specified as a time period and the severity of the water deficit as changes in soil water potential without considering the specific sensitivity of the respective phenological stage. We have shown in an earlier study that drought stress severity depends on the duration and magnitude of the water deficit, which are strongly depending on soil type and climatic conditions, and the sensitivity of the phenological stage (Hoelle et al, 2020). We propose a combination of absolute tuber yield under drought and tuber yield reduction relative to a well‐watered control to be suitable traits in identifying genotypes tolerant to drought.…”