2.04 DISEASE: PRE-HARVEST
Reduced sugar beet root health resulting from diseases of the growing sugar beet plant have been found to increase rates of quality loss during storage. A four year study over 47 fields by NBR in Sweden found correlations between post-harvest storage losses and the prevalence of the pathogen Aphanomyces cochliodes (Persson & Olsson, 2009). Campbell and Klotz (2006) compared root suffering from severe Aphanomyces root rot to those suffering from mild infections. They showed that sucrose loss during post-harvest storage for the roots with severe infection was approximately two to three times as large. The same research lab also compared resistant and non-resistant sugar beet grown in fields with the pathogen Beet necrotic yellow vein virus which causes Rhizomania (Campbell et al., 2008). The non-resistant varieties had increased loss of sucrose during post-harvest storage of some 20 percentage point (14 % compared to 34 %), and a near 20 fold increase in accumulated invert sugars. The same lab again has also examined Cercospora leaf spot, caused by the pathogen Cercospora beticola Sacc. (Karen Klotz Fugate et al., 2022). No differences in losses of quality during post-harvest storage were found. Strausbaugh et al. (2011) studied post-harvest storage systems which included roots from sugar beet infested with Rhizoctonia-bacteria complex and found increased rates of sucrose loss in piles with infected roots. A study ongoing during 2021 and 2022 with the Coordination Beet Research International (COBRI) of which NBR is a member, is investigating the impact on storability of three of the main viruses in the virus yellows complex. An infestation of beet yellows virus, beet mild yellowing virus, or beet chlorosis virus appears to lead to reduced quality during post-harvest storage. A 22 % increase in respiration during post-harvest storage at 5 °C is reported for roots from plants with virus yellows in Vukov (1977, Table 179, with reference to Neeb and Grupe (1960), Zucker., 13). The roots of plant affected with Beet necrotic yellow vein virus were found to freeze more readily than healthy roots (Strausbaugh & Eujayl, 2018). The roots affected by virus yellows, aphanomyces, rhizomania, and rhizoctonia, and the root of plants with cercospora leaf spot, all began post-harvest storage with lower quality (Campbell & Klotz, 2006; Campbell et al., 2008; Karen Klotz Fugate et al., 2022; Strausbaugh et al., 2011). A general conclusion on pre-harvest plant health is that a healthier plant will give healthier roots and better storability. A conclusion in Huijbregts et al. (2013) was that more work is needed around the pre-harvest factors driving root health and quality loss during post-harvest storage. This may include more focus on the incidences of pre-harvest diseases and on disease causing agents outside of those of economic importance to plant growth.