Flower-inducing technology facilitates speed breeding in cassava

Abstract

Cassava is a tropical crop that provides daily carbohydrates to more than 800 million people. New cassava cultivars with improved yield, disease resistance, and food quality are critical to end hunger and reduce poverty in the tropics. However, the progress of new cultivar development has been dragged down by difficulties obtaining flowers from desired parental plants to enable designed crosses. Inducing early flowering and increasing seed production are crucial to improving the efficiency of developing farmer-preferred cultivars. In the present study, we used breeding progenitors to evaluate the effectiveness of flower-inducing technology, including photoperiod extension, pruning, and plant growth regulators. Photoperiod extension significantly reduced the time to flowering in all 150 breeding progenitors, especially late-flowering progenitors which were reduced from 6-7 months to 3-4 months. Seed production was increased by using the combination of pruning and plant growth regulators. Combining photoperiod extension with pruning and the PGR 6-benzyladenine (synthetic cytokinin) produced significantly more fruits and seeds than only photoperiod extension and pruning. Another growth regulator, silver thiosulfate, commonly used to block the action of ethylene, did not show a significant effect on fruit or seed production when combined with pruning. The present study validated a protocol for flower induction in cassava breeding programs and discussed factors to consider in implementing the technology. By inducing early flowering and increasing seed production, the protocol helped move one step further for speed breeding in cassava.

Development of Methods for Improving Flowering and Seed Set of Diverse Germplasm in Cassava Breeding

“…The current greenhouse studies provide evidence for the role of the cytokinin BA in feminizing flower development, as reported in previous studies of cassava [23,25,32] and in Jatropha curcas L., which, like cassava, is in the family Euphorbiaceae [33], where the cytokinin Forchlorfenuron was effective. Indeed, in the present investigation, the percentage of female flowers increased from about 6-23% in STS-only treatments to over 89% in treatments that included BA (Table 1).…”

“…Phytodamage from high STS applications has long been recognized [17,29], and in field trials with cassava exposed to PGR treatments similar to those in the present study, authors describe phytodamage as a problem that limits treatment benefits [23,32]. Small young plants were particularly susceptible to BA and STS damage when applied at high concentrations.…”

“…Our goal has been to identify methods that provide tools for breeding programs to reliably and rapidly obtain progeny from a broad range of genotypes. In addition to producing more seed, obtaining seed at earlier tiers facilitates speed breeding, which is necessary for breeding methods with rapid one-year cycles [5,32]. However, our analysis does not evaluate the time and effort needed to monitor plants and apply treatments.…”

Identification of Genomic Regions for Traits Associated with Flowering in Cassava (Manihot esculenta Crantz)

“…Broad-sense heritability varied across traits, i.e., pistillates had the highest heritability ( H 2 = 0.83), followed by stem height at the first branch ( H 2 = 0.60). There are not many reports on broad-sense heritability estimates for flowering and associated traits in cassava; however, heritability estimates of over 0.80 were reported for plant height at first branch, number of branches, branching levels, as well as female flowers [ 11 , 73 , 74 , 75 ]. SNP-based heritability ( h 2 ) estimates were relatively higher for stem height at the first branch ( h 2 = 0.35), followed by branching ( h 2 = 0.25), and branching levels ( h 2 = 0.19).…”

SpeedFlower: a comprehensive speed breeding protocol for indica and japonica rice

“…Moreover, a speed vernalization protocol for winter crops like wheat and barley that allowed five generations per year was developed using SB conditions (Cha et al ., 2022 ). Recently, SB protocols with up to six generations were also optimized with different light conditions in the case of Cannabis sativa (Schilling et al ., 2023 ) and in cassava (Rodrmguez et al ., 2023 ).…”