Climatic Factors Associated with Flowering in Maize Germplasm of the Rainforest Agro-Ecology of Nigeria.

Maize (Zea maize L) is an important staple cereal produced in all agro-ecologies of West and Central Africa due to its popularity as hunger breaker in the drier savanna in addition to the forest and forest-savanna transition ecologies. A broad range of climatic conditions have been used to characterize the agro-ecological zones, including rainfall, temperature, length of the growing season, radiation and edaphic factors. The environments found in the tropical and sub tropical locations are extremely diverse. Environmental variability is a formidable challenge to Agronomists and Breeders when recommending suitable crops to poor-resource farmers in such marginal areas. The objectives of this study were to (i) determine the climatic factor associated with flowering of maize germplasm in the rainforest agro-climatic zone of sw Nigeria and (ii) classify the germplasm into maturity groups using the climatic factor. One hundred maize varieties were evaluated during the late and early cropping seasons of 2007/2008 and 2008/2009. Number of days to tasseling, anthesis and silking were recorded on individual plot basis. In addition, mean temperature, accumulated heat units (HU) and average sunshine hours (SH) to each flowering event were computed. Significant genotypic differences were observed for the flowering traits. There were also significant season and genotype x season interaction mean squares. TZEEPOPSTRCo, 97TZEE-Y-2C1 and SINETZEE-WSR with 46-50 days to flowering were identified as the earliest to flower. It took the varieties an average temperature of 25-25.230C, accumulated HU of 698-756.02, and average SH of 5.13-5.48 hrs to flower in the early cropping seasons. TZPB-SRPROLF1C3, BR9943-DMRSR and Oba-Super II with 66-71 days to flower were the latest to flower during the early seasons. These late maturing varieties used an average temperature of 25.55 oC -26.00oC, accumulated HU of 996-1074.33, and average SH of 6.00-6.20 hrs to flower. In the late season, 2004TZEE-WPOPSTRC4, TZEEPOPSTRCo, SINETZEE-WSR and TZE-WPOPDTSTRC4F2 with 46-51 days to flower were the earliest while BUSOLA STR, TZLCOMPCO, 9021-18STR and Oba super II with 62-67 days to flower were the latest. For the early maturing varieties flowering took an average temperature of 24.810C-24.840C, accumulated HU of 683.37-752.25, and average SH of 3.07-3.19 hrs while the late maturing varieties used average temperature of 25.100C-25.130C, accumulated HU of 921.87-1007.62 HU and average SH of 3.96 – 4.08 hrs.  Highly significant positive correlation coefficients were observed between the flowering traits and the climatic factors. Accumulated HU was the most effective climatic factor for classifying the 100 maize varieties into maturity groups.