Reproductive systems and low outbreeding barriers between Jacaranda cuspidifolia and J. mimosifolia (Jacarandeae, Bignoniaceae)

Abstract

The genus Jacaranda shows notable karyotype stability and a prevailing self‐sterile breeding system with evidence of late‐acting self‐incompatibility in several species. However, some studies have indicated self‐compatibility in J. mimosifolia, a species cultivated worldwide in tropical and subtropical areas. Jacaranda cuspidifolia is a closely related species with natural distribution broadly overlapping with that of J. mimosifolia, and manual heterospecific pollination studies have indicated that these species are interfertile, but there is no report on the breeding system of the former. In this study, we used hand‐pollination experiments, pistil longevity, epi‐fluorescence and histological analysis of post‐pollination events to determine the breeding system of J. cuspidifolia. We also employed intra and interspecific crosses and seed germination tests to reevaluate the breeding system of J. mimosifolia and the inter‐fertility between the two species. Some fruits were initiated from self‐pollinated pistils in J. mimosifolia, but none of them reached maturity. On the other hand, complete absence of fruit development by self‐pollination was verified in J. cuspidifolia, while in situ pollen tube growth and histological analysis of post‐pollination events in selfed pistils revealed the characteristic ovule penetration, fertilization and endosperm initiation also observed in other bignoniaceous species with late‐acting self‐incompatibility. Low outbreeding barriers seem to operate between these species because reciprocal interspecific crosses and hybrid seed germination tests indicated they are bilaterally interfertile. However, fruit/seed production and seed germinability were significantly lower when pistils of J. cuspidifolia were pollinated with pollen of J. mimosifolia, compared with crosses in the opposite direction, which indicates a partial unilateral incompatibility. This result is discussed in the context of the possible occurrence of self‐compatibility in J. mimosifolia. The low level of incongruity operating between the two species also points to their recent evolutionary divergence.

Unilateral cross-incompatibility between Camellia oleifera and C. yuhsienensis provides new insights for hybridization in Camellia spp

“…Unilateral cross-incompatibility(UCI) is defined as asymmetric reproductive isolation, manifested by successful crosses in one direction and unsuccessful crosses in the other ( Muñoz-Sanz et al., 2020 ). Currently, UCI has been observed in banana shrub ( Xu et al., 2017 ), jacaranda tree ( Bittencourt, 2019 ), azalea ( Okamoto and Ureshino, 2015 ), etc. However, no studies have been reported on the cytological mechanism of interspecific asymmetric hybridization in the genus Camellia between Camellia oleifera and Camellia yuhsienensis.…”

Reproductive biology of Jacarada ulei Bureau & K. Schum. (Bignoniaceae)

“…Anyway, obtainance of seeds may be complex, since the Bignoniaceae family is marked by floral self-incompatibility (Gandolphi and Bittencourt 2010). Regarding other species from Jacaranda genus, floral self-incompatibility was recorded for J. racemosa (Bittencourt and Semir 2006), J. copaia (Gurgel et al 2006, Jones and Hubbell 2006, Maues et al 2008, J. rugosa (Milet-Pinheiro & Schlindwen 2009), J. mimosifolia (Alves et al 2010, Bittencourt 2019, J. oxyphylla (Guimarães et al 2018), J. rugosa (Pontes et al 2022), while J. caroba showed some floral self-compatibility at a range of about 3% of self-pollinated flowers growing into mature fruits (Yanagizawa 1983, Guimarães et al 2008. The extension of floral self-incompatibility has not been recorded to Jacaranda ulei.…”