Abstract: Background and Objective: Wheat crop is among the leading cereals and its grain is used as a staple food in many countries of the world. Several environmental factors are effecting the performance of wheat crop. Late plantation of wheat crop in Pakistan is one of the factors that reduce the yield. The main aim of this study was to identify and select superior wheat genotype with good adoptability to sowing time under the current changing climatic scenario. Materials and Methods: The present study was carried out to screen newly developed wheat lines across different sowing dates to identify appropriate planting time for these new lines. A set of 7 wheat genotypes was planted on different sowing dates, starting from October, 25-December, 25 with 10 days interval. Results: Data analyses revealed significant effect of sowing time on overall performance of wheat genotype was observed. On the average, wheat crop sown till 15th of November gave better results whereas delayed sowing resulted in reduced grain yield. Similarly, the genotypes also exhibited significant variable performance across different sowing time. However Pr-128 performed well across all sowing dates and was also identified as stable genotypes in overall performance across various sowing dates. Conclusion: From the present study it could be suggested that the most optimum time for sowing of wheat crop is 5-15 of November. Moreover, the genotype Pr-128 in addition to normal sowing it can also be used as short duration variety in those areas where the wheat sowing is delayed due to late harvesting of other crops i.e., Maize, sugarcane etc.
INTRODUCTION
Wheat (Triticum aestivum L.) is an essential food crop in Asia as well as in many countries of the world. Its grain significantly contributed for human food supply and its straw for animal’s feed. In Pakistan, total area under spring wheat is 8.8 million hectares which produces 25.1 million tonnes grain/ year with average1 yield 2851kg ha–1. Like other provinces of Pakistan, wheat is also the major diet of the Khyber Pakhtunkhwa (KP). KP is food insecure region as it produced 1.15 million tons wheat annually against consumption of 2.9 million tons2. Improvement in wheat productivity at farm level would not only increase food security of farmer but also improve food availability at affordable prices in the province3. Average wheat grain yield of KP farmers is 1807 kg ha–1 that is far lower than national average wheat yield of Pakistan (2851 kg ha–1).
Late plantation of wheat crop is one of the limiting factors that reduce the yield. Therefore, sowing of wheat crop on proper sowing date play a key role to augment the production and avoid climate effects due to variations4. Several methodologies can be practiced for boosting up wheat productivity through the utilization of new high yielding disease resistant varieties and by adopting proper sowing date. Wheat is sown in winter which requires specific temperature and light for optimum growth5. If the temperature is above the optimum level much early plantation resulting in poor plants. Wheat growth and nutrient uptake efficiency of plants increases when sowing at optimum temperature. On the other hand delay sowing practices cause reduction in crop growth and yield6. It has been reported that early sowing of wheat enhances germination per unit area, plant height, spikelets/spike/grain/spike and weight of 1000 grains over late sowing7.
Sial et al.8, reported reduction in plant height, days to heading, maturity and grain yield due to late sowing of wheat crop. Sohail et al.9, reported that late sowing reduced the wheat grain upto 29%. Tahir et al.10, reported maximum grain yield at proper sowing date and lower grain yield in late sowing. Ali et al.11, investigated date of sowing effect on wheat grain yield and reported that wheat sown on November 10 gave highest grain yield. Delay in planting from November 20 gradually reduced the wheat yield. Ibrahim12 reported that most of time due to delayed planting, 86% losses in grain yield in short maturing varieties of 90-100 days has been observed. In this regards, Sial et al.8 determined appropriate crop yields associated with sowing dates in changing climate. Range of optimum planting date for different varieties varies with cropping husbandry and growing conditions of a particular region evaluated by sowing them at varying dates.
The Cereal Crops Research Institute (CCRI), Pirsabaq Nowshera KP in collaboration with CIMMYT Int. identify and selected several wheat varieties with high yield, improved quality and resistance to biotic and abiotic stresses. These newly developed wheat lines needs to be tested across different sowing dates to identify their response to varying environments. The environment is changing abruptly therefore screening of newly developed wheat lines under different planting dates is extremely important to test their potential. Today in the scenario of changing climate the interactions of G×E is big challenge for plant breeders to develop improved climate resilient wheat varieties. G×E interaction is a well-known methodology for identification adaptability and stability of genotypes. Researchers are always enthusiastic to develop a genotype that has stability in performance across environments13.
Thus, here, the importance of planting time for wheat was kept in mind and a set of newly developed wheat lines were evaluated across varying sowing dates using the GGE biplot technique proposed by Yan and Kang14 to recommend appropriate planting date and genotype (s) for irrigated areas of the KP. Keeping in view the importance of wheat and its lower yield due to varietal selection and late sowing in the country, the present study was conducted with aim to evaluate the yield potential of different advance lines/genotypes under various sowing time and to select the best for especially late sowing.
MATERIALS AND METHODS
Study area: The experiment was conducted at CCRI, Pirsabaq Nowshera (34 °N latitude, 72°E longitude and 288 m altitude) under irrigated conditions during 2017-18, 2018-19. The mean temperature and rainfall during the growing period is given in Table 1.
The experiment was comprised of 49 treatments of different sowing dates and genotypes combinations. Each genotype was planted in 6 rows while row to row separation was kept as 30 cm therefore, the area of individual plot was 9 m2. Two commercial wheat varieties i.e., Pirsabak-2013 and Khaista-2017 along with five advance lines namely PR-123, PR-125, PR-128, PR-129 and PR-130 (Table 2) were sown on seven different sowing dates i.e., October 25, November 5, 15, 25, December 5, 15 and 25 in a randomized complete block design replicated thrice. Uniform cultural practices were applied during both the years. The agronomic practices like seeding rate was applied at 100 kg ha–1, NPK at ratio of 120:90:60 kg ha–1 in form of Urea, DAP and MOP, respectively. Basal dose of DAP and MOP were applied at planting time while split doses of urea was applied as half sowing and other half at first irrigation15. Central four were selected for data recording on grain yield (t ha–1).
| Table 1: | Comparison of meteorological data during the growing cycle at CCRI for 2017-18 and 2018-19 |
| Table 2: | Parentage of wheat genotypes used in the study |
Statistical analysis: Analysis of variance procedure was followed for the statistical analysis of recorded data according to the model suggested by Annicchiarico16 for genotype by environment data combined over years. Least significant differences (LSD) test using 5% level of probability the means were equated. GGE-biplot, a graphical approach was also used to identify stability in performance of genotypes across different sowing dates as proposed by Yan and Kang14.
RESULTS
Grain yield: Data pertaining grain yield are given in Table 3. For grain yield, year main effect was significant (p<0.01). Average grain yield was significantly higher (5.1 t ha–1) during the year 2017, as compared to (4.6 t ha–1) 2018. Similarly genotypes differed significantly from each other regarding grain yield. In addition, the sowing date’s main effect and genotypes×sowing dates interaction were also found significant. Data regarding grain yield performance of wheat genotypes across different sowing dates over two years are presented in Table 4. Among the genotypes, PR-128 produced significantly higher grain yield during both years (5.5 and 5.0 t ha–1) whereas two genotypes produced the lowest grain yield 4.6 t ha–1 (PR-129) and 4.1 t ha–1 (PR-130) during the first and second year of experimentation, respectively.
| Table 3: | Mean squares for grain yield (t ha–1) of wheat genotypes evaluated across different sowing dates for 2 years |
| **Significant at 5, 1% level of probability, NS: Non-significant | |
Since, sowing dates×years effect was non-significant therefore average over both the years were taken into consideration. Wheat genotypes planted on 15th of November produced significantly higher grain yield (5.3 t ha–1) whereas it was reduced to 4.2 t ha–1 when plantation of genotypes was delayed till 25th of December. Data regarding effect of sowing time on grain yield of wheat genotypes is presented in Table 5. The present study indicated 2.9% increase when wheat plantation was shifted from 25th of October to 15th of November. However, delaying wheat sowing after 15th of November resulted in yield reduction which was found highest (-18.2%) during 25th of December.
Since, Genotype×Sowing date effect was found significant, therefore, mean yield data of genotypes across different sowing dates presented in Table 4 was further analyzed using GGE biplot analysis, so as to clearly visualize graphically the G×E interaction the existing.
| Table 4: | Pooled data regarding grain yield (t ha–1) of seven wheat genotypes evaluated under different date of sowing |
| LSD(0.05) for genotype = 0.1, LSD(0.05) for sowing dates = 0.1, LSD(0.05) for genotype×sowing dates = 0.3 | |
| Table 5: | Differences in grain yield (%) of wheat genotypes as influenced by different sowing dates combined over years |
| Fig. 1: | Polygon view of biplot regarding grain yield performance of 7 genotypes across 7 sowing dates |
| Fig. 2: | Biplot regarding stability and grain yield performance of 7 genotypes evaluated across 7 sowing dates |
All the genotypes in the biplot were arranged in such a way that some of them were on the vertices, while the rest were inside the polygon (Fig. 1) with some genotypes being the most responsive are placed on the vertices. Similarly, the different sowing dates are denoted in uppercase letters. The whole biplot is divided into various sectors and the most important one is between vertex 1 and 2 where all the sowing dates are present. In this sector genotype Pr-128 occupied position on the vertex which showed that it out classed all other genotypes in performance across all sowing dates. Moreover, the other genotype PS-13 also occupied position in the same sector therefore it is clear that it also performed better across all sowing dates. On the other hand the remaining genotypes occupied position in the opposite direction therefore it is clear that they did not performed well across different sowing dates.
The Fig. 2 demonstrates the average grain yield and stability in performance of various genotypes across different sowing dates. Mean performance in term of yield of wheat genotypes was calculated by the prediction of respective markers to the ATC X-axis (Single arrowed line), while consistency of wheat genotypes was approached by the projection of the respective markers to the ATC Y-axis. Moreover, ideal genotype status of genotypes via were compared using GGE biplot which is presented in Fig. 2 as the center of the concentric circle, representing wheat having the optimum grain yield across various sowing dates and was at best level in term of grain yield. Since, genotype Pr-128 and PS-13 is present in the center of the concentric circle therefore ranked on top regarding performance and stability whereas, Pr-123 and Pr-125 occupied second position being placed in the second concentric circle.
DISCUSSION
Since, wheat is the staple food of the country therefore special considerations are given for its yield improvement. However, the per unit area yield of wheat in country is comparatively low than other advanced countries. Besides others, improper wheat varieties for late plantation is one of the factors that reduce grain yield of wheat. During the present study fluctuation in yield of wheat was observed in late plantation which might be due to shorter duration of growth and development17. In one of the studies, Qasim et al.18, reported higher wheat grain yield when planted in early November whereas planted in late December drastically reduced wheat yield19. The reduction in wheat grain yield due to late plantation might be due to decreased growing period or less flexibility of genotypes to adapt to short growing period and exposure of plants to high temperature at terminal growth stage20. In a similar sort of experimentation conducted by Sharma et al.21, also supported the phenomena about yield reduction due to late sowing ranging from 30-40% compared with normal plantation. They further stated that, more grain yield produced by early planted wheat might be due to extended growth period for both vegetative and reproductive stages of the crop. The possible reason for this might be due to maximum utilization of resources during the plant growth stages viz. grain filling duration, growth behavior of crop, which subsequently result in accumulation of optimum dry matter due to delay plantation. In addition to this, the short of phenological development might be possible reason for utmost decreasing in various yield component and so is the final produce22,23. Other possible reason for low grain yield in late planted wheat might be due to increase in temperature24. Modarresi et al.25, also reported that high temperature could decrease grain yield upto 46%.
For analysis of multi sowing time data set, the GGE biplot is one of the advance and best possible ways to effectively identify G×E interaction. The GGE biplot visually demonstrate the performance of genotypes which enable the researcher to identify best suited genotype for specific environment or sowing time. The better way to know clearly the interaction patterns among wheat genotypes and date of sowing and to efficiently understand a biplot the polygon view of the biplot was used14. Genotypes more responsive to sowing time were visualized on the vertexes those having either the best or the poorest performance in one or all sowing date26. During this two years study, it has been found that genotype PR-128 on the average performed well across all sowing dates. It also outclassed the check cultivar PS-13 which is already recommended for late plantation therefore PR-128 on approval could be recommended to farming community especially in those areas where wheat plantation is delayed due to late harvesting of crops (i.e., Rice, sugarcane, Tobacco, potato etc). Moreover, it can also be used in future wheat breeding program.
CONCLUSION
The present study suggested that the most optimum time for sowing of wheat crop is 5-15th of November. The genotype PR-128 performed well across all sowing dates therefore upon approval as a variety it can be used as short duration variety in sugarcane, tobacco and potato growing areas where the wheat plantation is delayed due to late harvesting of these crops.
SIGNIFICANCE STATEMENT
This study discovers the optimum planting time for various wheat genotypes which could be useful as a guideline for planting suitable genotype on suitable planting date. Moreover, PR-128 can be a relatively good option to plant late in season with relatively less yield losses per unit area if sowing has been postponed till 25th November in the season. Under changing climatic conditions this study will help the researchers to develop the most promising wheat cultivars with relatively less yield losses per unit area due to delayed plantation. In addition, the PR-128 can be used as a potential parent in future wheat breeding programs.
ACKNOWLEDGMENTS
Authors are highly thankful of the US Agency for International Development (USAID) for the in-time financial support through the Agricultural Innovation Program (AIP) for Pakistan grant number AID-BFS-G-11-00002.