Vanilla bahiana hoehne (Orchidaceae): Studies on fruit development and new perspectives into crop improvement for the vanilla planifolia group

Abstract

Vanilla is the most well-known and economically important genus of Orchidaceae in the world. Vanilla bahiana is restricted to Brazil and its conservation status was recently assessed as ‘Endangered’. The species is phylogenetically closely related to V. planifolia, whose pods are the main natural source of vanillin. The primary desirable traits for vanilla production are high fruit set and great resistance to abiotic stress. High temperatures (> 32ºC) and heavy rain favor fungal infection, and thus are indirectly responsible for fruit drop by V. planifolia in cultivation. The aim of the present study was to follow the process of pod ripening of V. bahiana in a restinga fragment in an Environmental Protection Area of Bahia State, and to highlight implications for vanilla crop improvement. Fieldwork was carried out from April 2016 to January 2017. A total of nine manual self-pollinations and nine manual cross-pollinations were successfully carried out. Fruit length, diameter and girth were recorded every two weeks. Fruit permanence in the infrutescence was measured as consecutive days from pollination. Descriptive statistics were calculated and Pearson correlation analysis performed among all attributes per pollination method. The influence of temperature and rainfall was also analyzed. Pod measurements and fruit permanence in the infrutescence were higher for cross-pollination than self-pollination. Higher rainfall results in fruit drop. The use of V. bahiana in breeding efforts for the genus is here strongly suggested and supported by previously published studies that allowed us to highlight several desirable traits: vanillin production, its wide geographical distribution and occurrence in a variety of habitats; substantial populations; resistance to conditions of drought and high luminosity and temperature; extensive blooming period; high number of flowers per raceme; possible synchronised flowering with V. planifolia, and fruiting throughout the year. These prospects are promising and should be further evaluated, not only for V. bahiana but for other vanilla crop wild relatives. Studies of pollination ecology can be used to set guidelines for the conservation of the V. planifolia group and to encourage the development of strategies to increase the production of fruit and, consequently, vanillin for its culinary uses and medical applications.