Project

Grafting watermelon to interspecific hybrid rootstock reduces hollow heart disorder

Goal: 1) Identify grafting effects on postharvest fruit quality and the incidence and severity of hollow heart disorder in 'Liberty' watermelon
2) compare tissue firmness and tissue density (e.g., the number and size of fruit cells in the heart tissue) between grafting treatments and incidence of hollow heart via confocal microscopy
3) assess total pectin content and cell wall polysaccharide architecture to identify how graft and hollow heart effect cell wall strength and integrity

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Project log

Marlee Trandel
added a research item
Hollow heart (HH) fruit disorder develops predominantly in triploid (seedless) watermelon. Incidence of HH can range from 0 to over 60%, depending upon the season, making it difficult to predict or control. Fruit genetics, pollination, and other environmental factors are thought to contribute to the onset and development of HH. Previous research indicates that watermelon cultivars with lower tissue firmness have a higher incidence of HH. Grafting a watermelon scion to a hybrid squash rootstock has been shown to increase tissue firmness and may decrease HH in susceptible cultivars. In this study, ‘Liberty’, a HH susceptible cultivar, was grafted to the interspecific hybrid C. maxima x moschata rootstocks (RS) ‘Carnivor’ and ‘Kazako’, or to ‘Emphasis’ (Lageneria siceraria, bottle gourd RS). Fruit HH incidence was reduced by 28% when grafted to ‘Carnivor’ RS compared to non-grafted fruit. Flesh firmness was increased by 1 N in fruit from ‘Kazako’ or ‘Carnivor’ RS. The soluble solids content was lowest in fruit from the ‘Carnivor’ RS (11.7) or from fruit with HH (11.9), respectively. Fruit pH was slightly higher in those without HH and those from ‘Kazako’ or non-grafted RS. Lycopene, total sugars, citrulline or arginine content among grafting RS or with HH were not significantly different. Confocal micrographs from ripe heart tissue showed a decrease in the number of fruit cells with HH in non-grafted fruit or with ‘Carnivor’ RS but cell number increased in fruit from ‘Emphasis’ RS. Cell area was largest in fruit grafted to ‘Emphasis’ and in fruit with HH from ‘Carnivor’ or non-grafted compared to no HH (108,200 μm2). Our results show that fruit with higher tissue firmness had a lower incidence of HH and that grafting onto interspecific hybrid RS decreased HH incidence. These results indicate that grafting may be a useful technique to reduce HH disorder in varieties susceptible to HH.
Marlee Trandel
added a project goal
1) Identify grafting effects on postharvest fruit quality and the incidence and severity of hollow heart disorder in 'Liberty' watermelon
2) compare tissue firmness and tissue density (e.g., the number and size of fruit cells in the heart tissue) between grafting treatments and incidence of hollow heart via confocal microscopy
3) assess total pectin content and cell wall polysaccharide architecture to identify how graft and hollow heart effect cell wall strength and integrity