Breeding Procedures for Panicum maximum Jacq. Suggested by Plant Variability and Mode of Reproduction1

In 1970, spaced plants of 158 accessions of guineagrass (Panicum maximum Jacq.), supplied by the USDA Regional Plant Introduction Station, Experiment, Ga., were studied in detail at Tifton, Ga. Great variation was observed in all 12 characters studied. Plant height ranged from 53 to 248 cm and single green plant weight ranged from 0.09 to 6.13 kg. The in vitro dry matter digestibility (IVDMD) of complete culms at the early‐full‐head stage ranged from 41 to 72%. Most accessions set seed well when selfed under bag. Only 1.3% of the spaced plants survived the 1970‐71 winter (–8 C minimum), but 80% of the plants of PI 284764 from the Union of South Africa survived. A study of spaced‐plant progenies from 295 plants in the 1970 planting revealed that 87.8% were highly apomictic (showed no segregation). Facultative apomixis was present in 11.6% of the progenies. These carried 5 to 20% of offtype plants. Two sexual plants, discovered in facultative apomictic introductions PI 277946 and 277922, gave fertile hybrids when crossed with giant short‐day types. Seed shattering was heavy and similar in some 6,000 plants studied. Suggested breeding procedures include screening extensive ecotype collections from Africa and recombining in one or more genotypes (fixed by apomixis) the desirable genes currently available. Suggested procedures for obtaining genes for shatter resistance include mutation breeding, screening selfed progenies of sexual plants and advanced generations of sexual ✕ apomictic hybrids that may release shatter resistance genes hidden in the germplasm, and transferring shatter resistance from other Panicum species by interspecific hybridization.