UNPRECEDENTED VARIABILITY of climate is posing serious threats to crop production in Pakistan. An important example of such problem is unexpected early summer rainfall at harvesting of wheat crop since last few years. During current season, hailstorms were accompanied by torrential rainfalls at different growth stages of wheat for 2-3 times in different regions of the country. During wheat season 2014-15, we are facing 5-10 Mds reduction in grain yield per acre in different regions of the country where as a bumper crop was being expected at earlier stages. Crop yield can be termed as a function of climate, soil and crop management but this year unheralded climatic conditions are the major cause of this shortfall.
No doubt all stages from emergence to maturity have key contribution towards final grain harvest but the most important are anthesis and grain filling stages. Flag leaf is the terminal leaf to emerge in wheat plant enfolding spike in it and stays green until crop reaches to physiological maturity. During photosynthetic activity, flag leaf provides almost 60-70% synthates to developing grains therefore have a primal role in obtaining the higher crop yield. In wheat season 2014-15, cloudiness from mid February to mid March caused less sunshine hours available to crop plants ranging 1.5-3 hrs/day as compared to average of last 2 years ranging 7-9 hrs/day. This dimming of light causes reduction in photosynthetic activity in flag leaf and thus results in less weight per grain.
Rains made water available for wheat crop during unwanted period which extends the vegetative growth phase and crop did not shift to reproductive phase in time and emergence of flag leaf was delayed thus confining the time for grain filing. Swift winds along with heavy rains also caused lodging of crop in some districts like Gujranwala which cause shriveled and black colored grains thus also cause damage to the quality of produce along with quantity.
During wheat season 2014-15, hailstorm occurred in month of March resulting in physical damage to wheat crop. The modes of damage to wheat crop were, loopering of tops of wheat plant, poor pollination/fertilization, shattering of spikelet in early sown wheat crop, mechanical injury to Flag leaf and stem of wheat. Shattering of grains was also observed in October sown wheat crop.
High humidity and frequent rains are favorable conditions for increasing the fungal infection on both leaf blade and leaf sheath, even on spikes when in epidemic form especially when temperature is 25-30°C accompanied by 50 to 60 % Relative humidity. Wheat varieties become susceptible to Rust attack after 4-5 years, as Sehar-2006 (wheat variety) is being heavily attacked since last two years. But the intensity of infection was very low during this season because most of the area was under cultivation of newly evolved varieties viz Galaxy-2013, Punjab-2011, Millat-2011, AARI-2011 and AAS-2011. These varieties are quite resistant to fungal diseases (Leaf, Stripe and Stem Rust). So, Rust (fungal attack) cannot be enlisted as major cause of low yield in this year (fortunately).