Studies on reproductive strategies of Vitex negundo L. var. heterophylla (Franch.) Rehder (Lamiaceae) based on morphological characteristics and SSR markers

Abstract

Vitex negundo L. var. heterophylla (Franch.) Rehder (Lamiaceae) is an important tree species for soil and water conservation, yet the reproductive ecology of this species remains to be elucidated. To investigate the reproductive traits of V. negundo var. heterophylla, the phenology, morphological characteristics (a suite of characters was assessed: floral morphology, nectar production, pollen viability, and stigma receptivity) and mating system of this species were systematically revealed for the first time in this study. Phenological observations, morphological measurements, and nectar production analysis were conducted during anthesis. Pollen viability and stigma receptivity at different flowering stages were measured by biochemical methods. Finally, genetic analysis based on SSR markers was used to reveal the mating system; outcrossing index and pollen‐ovule ratio were also calculated to help analysis. V. negundo var. heterophylla showed several obvious characteristics of outcrossing, such as abundant and attractive flowers, secreting nectar, and emitting scent. In addition, mechanisms such as homogamy and a short anther‐stigma distance that can promote self‐fertilization were also identified in this species. The coexistence of selfing and outcrossing characteristics demonstrates a predominantly outcrossed mixed mating system (outcrossing rate, t = 95%). The scientific information provided by this study may contribute to conservation of V. negundo var. heterophylla from a reproductive perspective.

Mating strategies of Vitex negundo L. var. heterophylla (Franch.) Rehder (Lamiaceae): A mixed mating system with inbreeding depression

“…heterophylla is a constantly 25%, which means that only one of the four ovules can fully develop and bear fruit, and the other three will be aborted due to late zygotic competition. The same phenomenon is found in V. fischeri (Lengkeek et al, 2006) and V. Doniana (Sinebou et al, 2016) is also reported. This is not due to pollen limitation, but may be related to resource allocation.…”

“…Vitex negundo L. var. heterophylla has a bilabial flower that is symmetrical, and the lower lip of the bilabial corolla is flat and broad, which can be used as a comfortable platform for insects to forage (Sun et al, 2020). A similar situation also occurred in Thalictrum pubescens, an ambophilous (both zoophily and anemophily) species that probably represents a transitional state in the evolution of anemophily.…”

“…A similar example would be Echium wildpretii (Boraginaceae) on Tenerife, Canary Islands. Researchers investigated the fitness of progeny from experimental self-and cross-pollination in eight populations of different size of E. wildpretii, and found that seed set of open-and hand-outcrossed-pollinated flowers was higher in large than in small populations, possibly due to more frequent biparental inbreeding in the latter (Sedlacek et al, 2012). Through the study on combining the analysis of floral morphology, behavior of flower visitors, and artificial pollination, the reproductive characteristics of the Ziziphus jujuba var.…”

Mating strategies of Vitex negundo L. var. heterophylla (Franch.) Rehder (Lamiaceae): a mixed mating system with inbreeding depression.

“…heterophylla can produce mature fruits under both outcrossing (the highest fruit-setting rate) and selfing strategies, indicating that V. negundo L. var.heterophylla presents a mixed mating system with mainly outcrossing and self-compatibility. It is consistent with the conclusion of Sun et al (2020) based on the hybridization index and pollen ovule ratio.…”

“…Bagging is carried out at the bud stage, and according to the pollen vigor and stigma pollination at different stages after flowering, and the best pollination time is determined to be from 10:00 am to 12:00 am (Sun et al, 2020). With the help of tweezers, the anther directly contacts the stigma for pollination.…”