Rootstock influences postharvest anthracnose development in 'Hass' avocado

Abstract

Rootstock studies conducted on ‘Hass’ avocado found that rootstock had a significant impact on postharvest anthracnose susceptibility. This is the first record of such an effect for avocado. The severity and incidence of anthracnose was significantly lower on ‘Hass’ grafted to ‘Velvick’ Guatemalan seedling rootstock compared with the ‘Duke 6’ Mexican seedling rootstock. Differences in anthracnose susceptibility were related to significant differences in concentrations of antifungal dienes in the leaves and mineral nutrients in the leaves and fruits from trees grafted to different rootstocks. Leaf diene concentrations were up to 1.5 times higher in ‘Hass’ trees on the ‘Velvick’ than the ‘Duke 6’ rootstock. In ungrafted nursery stock trees, diene concentrations were around 3 times higher in ‘Velvick’ than ‘Duke 6’ leaves. The ‘Velvick’/‘Hass’ combination also had a significantly lower leaf N concentration, a significantly higher fruit flesh Mn concentration, and significantly lower and higher leaf N/Ca and Ca+Mg/K ratios, respectively. A significant correlation (r = 0.82) between anthracnose severity and skin N/Ca ratio was also evident.

Effects of clonal rootstocks on ‘Hass’ avocado yield components, alternate bearing, and nutrition

“…In general, Guatemalan rootstocks (i.e., the G755 series, and G1033) had higher Ca and Mg, but lower N, than the Mexican rootstocks. Willingham et al (2001) also found that a Guatemalan rootstock had lower leaf N than a Mexican rootstock. Haas (1950a,b) found that seedling Guatemalan-race rootstocks had higher Ca than seedling Mexican-race rootstocks.…”

Between-tree variation in fruit quality and fruit mineral concentrations of Hass avocados

“…Similar season or site effects on the correlations between Hass fruit quality attributes and flesh Ca, Mg, and K concentrations have been observed in New Zealand (Thorp et al 1997) and Australia (Hofman et al 2002;Vuthapanich 2001), with some sites showing strong correlations between fruit mineral concentrations and fruit quality in some years, but not in other years or in other sites. As the avocado industry in Australia is currently based on seedling rootstocks of unknown origin, it has been suggested that rootstocks may be a major contributing factor in the high between-tree variability in avocado quality and fruit minerals, and may present an important mechanism to improve avocado quality (Willingham et al 2001).…”

“…Scion leaf concentrations of K, N and Mg can also be affected by rootstock race. Recent reports suggest that avocado rootstock can also affect fruit Ca concentration, the ratio of (Ca + Mg):K in the fruit, and fruit quality (Willingham et al 2001;Marques et al 2003).…”

Rootstock scion somatogenetic interactions in perennial composite plants

“…Anthracnose is a serious post-harvest fungal disease in avocado that leads to rotting of the fruit. Willingham et al (2001) tested ‘Hass’ scion on two rootstocks for their influence on anthracnose. After post-harvest ripening at 22 °C, fruit from 3.5- and 8-year-old trees demonstrated significant differences in both disease incidence and severity.…”