Microspore developmental evaluation at the booting stage and androgenic callus induction in sorghum [Sorghum bicolor (L.) Moench] via anther culture

Androgenesis is a key method for producing doubled haploid (DH) lines, typically achieved through in vitro techniques such as anther culture and isolated microspore culture. This study aimed to determine the microspore developmental stages associated with specific spikelet positions during the booting stage (BS), evaluate the response of several sorghum genotypes to androgenic callus induction, and examine the effect of putrescine on callus formation success in sorghum anther culture. Spikelet and anther length were measured, and microspore developmental stages were determined under a microscope on the anthers of apical, middle, and basal spikelets at different sampling times during the BS. Anthers containing early uninucleate (EU) microspores were inoculated on callus induction media based on MS medium supplemented with 2.0 mg l-1 NAA + 0.5 mg l-1 kinetin, with and without 10-3 M putrescine. The results showed that spikelet and anther length in specific panicle positions were positively correlated with microspore developmental stage. This provides practical morphological indicators to identify the EU microspores stage in sorghum without microscopy by observing morphological changes in the size, shape, and color of spikelets and anthers during the booting stage. In this research, microspores at the EU stage were predominantly (> 80%) present in anthers from spikelets collected from the apical part of the panicle on day 2 of the BS. The success of androgenic callus induction via anther culture is still influenced by genotype dependency, with ‘Bioguma 1’ showed the greatest response among the evaluated genotypes at 9.69%. Additionally, an induction medium without putrescine was more effective at producing androgenic calli in sorghum anther culture.