Flowering and Fruit-set in Cassava under Extended Red-Light Photoperiod Supplemented with Plant-Growth Regulators and Pruning

Abstract

Background: Cassava (Manihot esculenta Crantz) is staple food and major source of calories for over 500 million people in sub-Saharan Africa. The crop is also a source of income for smallholder farmers, and has increasing potential for industrial utilization. However, breeding efforts to match the increasing demand of cassava are impeded by its inability to flower, delayed or unsynchronized flowering, low proportion of female flowers and high fruit abortions. To overcome these sexual reproductive bottlenecks, this study investigated the effectiveness of using red lights to extend the photoperiod (RLE), as a gateway to enhancing flowering and fruit set under field conditions. Methods: Panels of cassava genotypes, with non- or late and early flowering response, 10 in each case, were subjected to RLE from dusk to dawn. RLE was further evaluated at low (LL), medium (ML) and high (HL) red light intensities, at ~ ≤ 0.5; 1.0 and 1.5PFD (Photon Flux Density) in µmol m-2 s-1 respectively. Additionally, the effect of a cytokinin and anti-ethylene as plant growth regulators (PGR) and pruning under RLE treatment were examined. Results: RLE stimulated earlier flower initiation in all genotypes, by up to 2 months in the late-flowering genotypes. Height and number of nodes at first branching, particularly in the late-flowering genotypes were also reduced, by over 50%. Number and proportion of pistillate flowers more than doubled, while number of fruits and seeds also increased. Number of branching levels during the crop season also increased by about three. Earlier flowering in many genotypes was most elicited at LL to ML intensities. Additive effects on flower numbers were detected between RLE, PGR and pruning applications. PGR and pruning treatments further increased number and proportion of pistillate flowers and fruits. Plants subjected to PGR and pruning, developed bisexual flowers and exhibited feminization of staminate flowers. Pruning at first branching resulted in higher pistillate flower induction than at second branching. Conclusions: These results indicate that RLE improves flowering in cassava, and its effectiveness is enhanced when PGR and pruning are applied. Thus, deployment of these technologies in breeding programs could significantly enhance cassava hybridizations and thus cassava breeding efficiency and impact.

Speedy benthi: Elongated photoperiods reduce generation times of the model plant speciesNicotiana benthamiana

“…Other speed breeding approaches used fertilization to counteract possible stress responses and/or nutrient deficiencies (Ghosh et al, 2018). Moreover, the use of a far-red light spectrum was shown to additionally reduce the generation time for some crop plants (Ghosh et al, 2018;Baguma et al, 2023).…”

“…Other speed breeding approaches used fertilization to counteract possible stress responses and/or nutrient deficiencies (Ghosh et al, 2018). Moreover, the use of a far-red light spectrum was shown to additionally reduce the generation time for some crop plants (Ghosh et al, 2018; Baguma et al, 2023). We speculated that fertilization (Supplemental Data 3) could alleviate the yellowing phenotype observed under SB conditions (Figure 1,) and in combination with the use of a far-red light spectrum (Supplemental Data 4) could further reduce the generation time of N. benthamiana .…”

Assessment of Cassava Pollen Viability and Ovule Fertilizability under Red-Light and Plant-Growth-Regulator Treatments

“…However, the effect of PGR, especially BA and STS, on pollen viability or stainability and capability of pollen to cause ovule fertilization in plants has not been widely explored, and besides literature about such is scanty. Whereas BA was reported to induce flowering or feminization of flowers, STS increased abundance and prevented abortion of flowers, thus enhancing fruit and seed set in cassava [22,39,40]. However, the effects of these PGRs on pollen viability and ovule fertilizability in cassava were not analysed.…”

“…Three sets of plant materials (each consisting 10 genotypes), were subjected to red light (RL-), plant growth regulators (PGR-) and nontreatment (Non). The RL treatment was administered as described in [22]. In this case the study genotypes were subjected to a RL system setup using 50W light emitting diode (LED) lamps with red LEDs (model 5-10x5w, China) (illumination range 640-660nm) and with reflectors (339 × 350mm, model ISL-RFGB, CCS Inc., China) as sources of RL for extension of the photoperiod during the night.…”

“…On the other hand, application of red and blue lights (ratio of 1:1) were used to increase pollen viability in tomatoes [20] as blue and yellow lights promoted pollen germination in Peltophorum [21]. In cassava, field applications of RL photoperiod extension and PGRs (BA and STS), have been reported to enhance fruit and seed set [22] but there was no any effort made to explore their possible effects on pollen viability and ovule fertilizability. And yet, pollen viability may be an important factor and selection criterion for cassava breeders.…”