Itchgrass (Rottboellia cochinchinensis) Biotypes in World Populations

Abstract

Itchgrass biotypes from 34 countries or territories were evaluated under controlled and natural day length at Houma, LA. They could be placed in five broad groups based primarily on the effect of day length on flowering but also on general morphology and pattern of growth. The Group 1 biotypes (Argentina, Bolivia, Costa Rica, Cuba-1, Ecuador-1, Florida, Guadeloupe, Honduras-1, Louisiana-1, North Carolina, Papua New Guinea-1, Panama, Peru, Philippines-1, and Venezuela) were not affected by day lengths of 12 and 14 h (day length neutral) and flowered 35 to 57 d after germination. The Group 2 biotypes (Australia, Kenya-1, Reunion, South Africa, and Zimbabwe) also were not greatly affected by photoperiod and flowered 54 to 67 d after germination, and were taller with fewer and larger diameter culms than the Group 1 biotypes. The Group 3 biotypes (Brazil, Colombia, Jamaica, and Philippines-2) were moderately sensitive to photoperiod. They took longer to flower at 14 h than at 12 h and flowered in 63 to 95 d. The Group 4 biotypes (Cuba-2, Dominican Republic, Ecuador-2, Honduras-2, India, Louisiana-2, Malaysia, Papua New Guinea-2, Puerto Rico, Taiwan, and Thailand) were short-day plants that did not flower in the screenhouse until August or September (130 to 163 d), after the natural photoperiod had decreased to 13 h. The Group 5 biotypes (Indonesia, Kenya-2, Nigeria, Sudan, Tanzania, and Trinidad) were strict short-day plants that flowered only in September to November (167 to 226 d), after the day length had decreased to about 12 h. Most biotypes were diploids with 2n = 20 chromosomes, but some were polyploids (2n = 40 or 2n = 60). The shape of the glume tip on the pedicellate spikelet was found to be acuminate, acute, or obtuse for the biotypes with 2n = 20, 40, and 60 chromosomes, respectively, and was a reliable marker to distinguish diploids from polyploids.