Neck shrivel in European plum: Mechanisms and causes

• Applicant: Professor Dr. Moritz Knoche
• Subject Area: Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: from 2020 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 436553869

Neck shrivel is a physiological disorder of European plum fruit characterized by a shriveled pedicel-end and a turgescent stylar-end. It develops pre-harvest and continues postharvest. Affected fruit are perceived as poor quality, so are of low commercial value. Cultivar (genetic) differences exist in susceptibility to neck shrivel. Little is known of the mechanistic basis of neck shrivel. Increased transpiration through microcracks in the cuticle of the stem-end contributes to neck shrivel. However, at present it is not known whether this is the only reason for neck shrivel. Also, the mechanism of microcrack formation in the stem end and the absence thereof in the stylar end of the symmetric plum fruit is unknown. Empirical observations suggest water relations may play a role. Two hypotheses may be thought of that account for neck shrivel: Hypothesis 1 – The stem end, but not the stylar end has a negative water balance in symptomatic fruit. There is no such difference in non-symptomatic fruit. Hypothesis 2 – A gradient in osmotic potential from the stem end (less negative) to the stylar end (more negative) causes a redistribution of water from the stem end to the stylar end. The objective is to test the validity of these hypotheses. We will focus on the following items: (1) Why do microcracks, that are the primary reason for increased transpiration of the stem end, form at the stem end, but at not the stylar end although the fruit is largely symmetric (hypothesis 1 – negative water balance due to increased transpiration)(2) Differential vascular water transport in the xylem that feeds the stylar end of susceptible cultivars, but not or to a lesser extent the stem end (hypothesis 1 – negative water balance due to reduced vascular inflow), and (3) Gradients in water potential, osmotic potential and turgor between stem end and stylar end in susceptible cultivars (hypothesis 2 – internal redistribution due to gradients in osmotic potential). Understanding the mechanism of neck shrivel is a prerequisite for (1) breeding new, less-susceptible plum cultivars and (2) developing cultural measures that might decrease the incidence of neck shrivel. We expect the information generated to be applicable to many other fleshy fruit crop species, from cool temperate regions to the tropics.

• DFG Programme: Research Grants