RESPONSIVENESS OF WHEAT VARIETIES TO CHILLING PERIOD AND DEVELOPING TEMPERATURE-BASED SOWING MODEL

Abstract

Climatic conditions in the rainfed region have always been a critical problem for the successful sowing of wheat. Drought because of insufficient rains or excess of soil water due to heavy rains may create problems for the sowing of wheat in the rainfed region. Similarly due to late harvesting of cotton crop in southern Punjab, wheat (Triticum aestivum L.) sowing is delayed. In such situations, chilling (vernalization) requirement of wheat is not fulfilled. Hence farmer has to face a substantial yield loss. Vernalization is the exposure of plants to low temperature which increases the plants readiness to flower. The first part of the experiment was conducted to quantify the chilling requirement (VDs) of wheat cultivars under controlled conditions. Three different low temperatures of 3, 6 and 9oC in combination with five different durations of 7, 14, 21, 28 and 35 days were used as sources of VDs treatments. Vernalization days (VDs) were calculated by multiplying daily GDD value with effectiveness factor using CERES wheat model equations. An easy to use growth chamber-green house procedure was developed to determine the VDs requirement of different wheat cultivars. Two different sets of wheat cultivars were used in this study consisting of five spring wheat types from Pakistan, one spring and one winter type wheat cultivars from USA. Final leaf number (FLN), number of tillers plant-1, days to booting stage, days to heading initiation, days to complete head emergence, number of florets spikelet-1, time the spike remains green, number of spikelets spike-1, number of grains spike-1, total crop duration, spike length (cm), 100-grain weight (g) and grain yield per plant (g plant-1) were measured. If farmers have prepared the field for wheat plantation well in time they can either go for Inqilab-91 (a high VD-requiring wheat cultivar) or Sehar-06 (a low VD-requiring wheat cultivar) but in case of late plantation Sehar-06 would be the best management decision ensuring good yield. In the second part of experiment, study on gene combinations responsible for vernalization (Vrn-A1, Vrn-B1, Vrn-D1and Vrn-B3) was carried out. Information of varietal difference at gene level can successfully be used in future breeding programmes. In third part of the study, immature wheat embryos were successfully cultured on MS media for regeneration. Sehar-06 was selected for this study because of its high yield potential with low VDs requirement. After chilling treatment in lab as determined in first part, seedlings were transferred to pots in green house under controlled temperature conditions. Sehar-06 took 132 days to reach at immature stage by tissue culture. Thus 2-3 wheat generations can be completed in one year through lab greenhouse protocol. Green house results indicate that cultivars can be classified into three groups depending upon their VDs requirement (1) winter types which cannot enter into reproductive phase with 35 days of chilling treatment at 3 to 9oC (2) Low VD- requiring spring wheat cultivars which can head without vernalization and having a VD-saturation point with 7 days of chilling treatment at 3 to 9oC for optimum yield (3) High VD-requiring spring wheat cultivars which can head without vernalization and having a VD-saturation point with 14 days of chilling treatment at 3 to 9oC for optimum yield. By increasing VDs, days to booting stage, days to heading initiation, days to complete head emergence, time the spike remains green, number of spikelets spike-1 and total crop duration were increased in a linear way in all spring type wheat cultivars as compared to their controls. Differential response was observed in all wheat cultivars for final leaf number (FLN),number of florets spikelet-1 and number of spikelets spike-1 at all three temperatures. Grain yield per plant, number of grains spike-1, 100-grain weight (g), spike length (cm) and number of tillers plant-1 were increased upon increasing the extent of cold exposure up to VD-saturation point of every spring type wheat cultivar as compared to their controls. However, yield starts declining after VD-saturation point. Sehar-06 and Marquillo are low VDs requiring while GA-2002, Inqilab-91, Chakwal-50 and Fareed-06 are high VDs requiring spring wheat cultivars. Yield response of all wheat varieties under study at 3, 6 and 9oC against the chilling treatments was regressed individually. Equations were developed which explain the yield response with reasonable accuracy under control conditions. However, it is recommended to test these equations repeatedly over years to predict the yield response accurately for the wheat cultivars to grow them successfully both in green house and field conditions.