Effect of Pruning Young Branches on Fruit and Seed Set in Cassava

Marcela Pineda,Benchi Yu,Yinong Tian,Tim L Setter,Peter T Hyde,Sandra Salazar,Hernán Ceballos,Nelson Morante

doi:10.3389/fpls.2020.01107

Abstract

Flowering in cassava is closely linked with branching. Early-flowering genotypes branch low and abundantly. Although farmers prefer late flowering genotypes because of their erect plant architecture, their usefulness as progenitors in breeding is limited by their low seed production. In general, the first inflorescence aborts in cassava. Preventing this abortion would result in early production of seeds and make cassava breeding more efficient. The objective of this study was to assess if pruning young branches prevents the abortion of first inflorescences and promotes early fruit and seed set. Four genotypes with early, late, very late, and no flowering habits were grown under an extended photoperiod (EP) or normal dark night conditions (DN). Additional treatments included pruning young branches at the first or second flowering event and spraying (or not) benzyladenine (BA) after pruning. One genotype failed to flower and was not considered further. For the remaining genotypes, EP proved crucial to induce an earlier flowering, which is a pre-requisite for pruning. Total production of seeds in EP plots was 2,971 versus 150 in DN plots. For plants grown under EP, the average number of seeds per plant without pruning was 3.88, whereas those pruned produced 17.60 seeds per plant. Pruning at the first branching event led to higher number of seeds per plant (26.25) than pruning at the second flowering event (8.95). In general, applying BA was beneficial (38.52 and 13.98 seeds/plant with or without spraying it, respectively). The best combination of treatments was different for each genotype. Pruning young branches and applying BA in the first flowering event not only prevented the abortion of inflorescences but also induced the feminization of male flowers into hermaphrodite or female-only flowers. The procedures suggested from this study (combining EP, pruning young branches, and spraying BA), allowed the production of a high number of seeds from erect cassava genotypes in a short period. The implementation of these procedures will improve the breeding efficiency in cassava.

Highlights

Cassava (Manihot esculenta Crantz) has significant economic relevance, in the lowland tropics
The largest number of seed per plant obtained across the entire experiment came from plants of this clone, pruned in the first branching event, and with the addition of BA
The unquestionable conclusion is that the combination of extended photoperiod (EP), pruning in the first branching event with the additional spraying of BA maximizes the early production of seed of this very late flowering cassava genotype

Summary

Introduction

Cassava (Manihot esculenta Crantz) has significant economic relevance, in the lowland tropics. Its main product is the starchy roots that are harvested, usually, about 12 months after planting (MAP). It is a fundamental food security crop in many regions of the world, Sub-Saharan Africa. What is commonly identified as a male flower is an inflorescence of 10 single-stamen flowers. These inflorescences, known as cyathia, are protected by petal-like bracts. Male and female cyathia will be treated in this article as if they were single flowers as the distinction is only relevant from the botanical point of view. Cassava is a diclinous and monoecious species producing either female (pistillate) or male (staminate) flowers in terminal inflorescences (racemes or panicles) within the same plant. Hermaphrodite flowers can be observed but at very low frequency (Perera et al, 2012)

Objectives

Methods

Results

Discussion

Conclusion