Variability of the photoperiod response in guar (Cyamopsis tetragonoloba (L.) Taub.) genotypes of different geographic origin

Abstract

The introduction of the new legume crop guar is of great practical importance for Russia, since it serves as a source of valuable vegetable raw material, guar gum, used for the food, gas and oil industry. The main problem with guar cultivation in the southern regions of the Russian Federation is that this plant should be grown under a short photoperiod. Prolonged daylight exposure is an obstacle to the timely transition of guar to flowering, which dramatically affects its productivity. In the study, 192 guar genotypes from the VIR collection were tested for the speed of transition to flowering on an extremely long photoperiod (18.2-18.9 h) in the greenhouse of the Pushkin experimental station of VIR (St. Petersburg). At the same time, the earliness of maturation of the same genotypes was estimated under the field conditions in the Kuban experimental station of VIR (Krasnodar area). Among the samples tested, genotypes with weak photoperiodic sensitivity (which were also early maturated under the conditions of Krasnodar), as well as the highly photoperiod-sensitive genotypes were identified. It has been established that for the same guar plant the critical photoperiod initiating the formation of buds may not coincide with the critical photoperiod required for their flushing (i. e. flowering per se). The observed fact confirms the hypothesis reported earlier about a two-stage launch of the flowering program in guar, according to which budding and flowering itself are controlled by independent gene systems. According to our results, the successful breeding of early mature guar varieties ultimately depends on the first gene system that controls the initiation of budding in response to a critical photoperiod. We suggest that another hypothetical gene system can influence the dates of guar flowering, which determines the speed of vegetative development of a specific genotype, measured as the number of days from germination to the appearance of the first true leaf. Thus, sensitivity to photoperiod in guar is only one of several factors that determine the speed of a plant's transition to flowering, and it should not be assessed on the basis of the length of the period from germination to flowering, which is common in breeding practice. The results of the study show that, although the photoperiod sensitivity of guar limits the range of geographic latitudes in which the legume crop can be successfully grown, there is a real opportunity to overcome this limitation by selecting and propagating photoperiod-insensitive genotypes from the enormous genetic diversity of this species.

Key metabolites associated with the onset of flowering of guar genotypes (Cyamopsis tetragonoloba (L.) Taub)

“…Among them 30 genotypes have formed the floral buds early enough (days from the appearance of the first true leaf up to first floral bud = 41 ± 1.8, mean ± SE). For the other 52 photoperiod-sensitive genotypes, the prolonged daylight caused obstacles to the transition to a flowering program, which led to a strong delay in the formation of floral buds (95 ± 1.7, mean ± SE) [ 4 ]. We investigated metabolomic profiles of tissues of the third true leaves for plants from the two contrast groups of «early flowering» and «delayed flowering» guar genotypes (Additional file 1 ).…”

“…In our experiment 96 guar genotypes, each presented by 8 individuals, have been grown under conditions of the greenhouse of the Pushkin branch of VIR during six months (May -October) at the photoperiod that is natural to the latitude of St. Petersburg (59°53′39″N). The experiment allowed us to monitor the reaction of different genotypes of the short-day crop to a gradually decreasing length of daylight: from the maximum (~19 h) on the day of the summer solstice, to a relatively short (11 h) in the first decade of October [4]. We had an opportunity to observe how the guar plants one by one passed to flowering as soon as the photoperiod reached a certain threshold level specific for a particular genotype.…”

“…As previously reported, the genotype was recorded as "early flowering" if it turned to flowering within 41 ± 1,8 from the first true leaf appearance. Correspondingly, a genotype was assigned to the "delayed flowering" group if it switched to flowering late (after 95 ± 1,7 days) [4].…”

“…Besides the determinate and indeterminate growth habits, a particular daylight length significantly affects the onset of flowering in guar [3]. In turn, day-neutral guar genotypes usually mature earlier than those with high sensitivity to the length of photoperiod [4].…”

Growth stages and developmental patterns of guar

“…These observations are helpful in understanding the growth habits and phenological variation of guar but will not provide specific expectations on the timing of developmental progression in any particular system, guar variety, or year. It is important to note that guar has photoperiod sensitivity, and is observed to be a short‐day plant (Lubbers, 1987; Teplyakova, Valkov, Dzyubenko, & Potokina, 2019), which will affect reproductive development, depending on the growing environment. The alternative name of guar, clusterbean, is based on the reproductive growth habit of the plant in which pod formation occurs in clusters on reproductive stems.…”