In vitro regeneration from leaf-base segments in three genotypes of Urochloa spp.

Abstract

The key agricultural species of Urochloa P.Beauv. (signal grass), important as tropical forage grasses, are characterised by asexual seed formation (apomixis), and this presents a challenge for breeding programs. Biotechnological approaches could be an option to develop improved cultivars. We evaluated the regenerative potential from three commercial genotypes, U. brizantha cv. Marandu, U. decumbens cv. Basilisk and U. ruziziensis cv. Ruziziensis, by using leaf-base segments as explants. We tested two auxins (2,4-D and picloram) and one cytokinin (TDZ) at four concentrations (1, 2, 3 and 4 mg L–1). Seeds were scarified, peeled and disinfected before inoculation on half-strength MS media in the dark for 14 days. Leaf-base explants were sectioned in thin slices and inoculated into the media. We analysed the number of primary calluses, number of calluses with shoots clusters and the average of regenerated plants. The lowest concentration of auxins tested (1 mg L–1) yielded the highest number of regenerated plants for Marandú and Basilisk, whereas the optimum for Ruziziensis was 2 mg L–1. Medium with higher concentrations of TDZ (4 mg L–1) was required to produce high frequency of plants for all genotypes. Explants cultured on media with TDZ produced very few calluses. These results indicate that the auxins and cytokinin tested can induce plant regeneration from Urochloa leaf-base segments, and may be used to produce transgenic plants in genetic transformation studies.

Genetic Transformation of Apomictic Grasses: Progress and Constraints

“…U. brizanthaand U. decumbens were the genotypes that were most prone to somatic embryogenesis, whereas U. humidicola and U. ruziziensis showed a minimal response. Similar results were obtained by Yaguinuma et al (2018) using leaf base segments as explants. In U. decumbens, 1 mg/L of picloram was more effective in regenerating plants than 1 mg/L of 2,4-D (49 vs. 14%), and U. ruziziensis tended to be more recalcitrant for plant regeneration.…”

Leaf transformation for efficient random integration and targeted genome modification in maize and sorghum

“…However, the above progress continues to rely on immature embryo transformation, which has been a constraint for many grass family crops, motivating researchers to explore alternative explants for tissue culture and transformation. The leaf base has been an attractive tissue culture explant for almost four decades, with callus initiation and regeneration being demonstrated in numerous Poaceae species including wheat [41][42][43][44] , oat 45,46 , barley 47,48 , rye 49 , maize 23 , rice 50 and various apomictic grasses 51 . Accordingly, researchers have used leaf bases to generate embryogenic callus as the target explant for Agrobacterium infection and the regeneration of transgenic plants-for example, in maize 23 , indica rice 24,52 , Ma bamboo 25 and teosinte 26 .…”