Role of Free and Bound Phenols with Certain Field Factors in the Population Density of Aphid Species and Onion Thrips Attacking Bread Wheat Cultivars under Drought Conditions

Abstract

The experiment of five of bread wheat cultivars (Sahel 1, Seds 4, Gemaza 9, Giza 168, and Misr 2) were investigated during (2015- 2016 and 2016- 2017) at the farm of Faculty of Agriculture, Assiut University, Assiut, Egypt. The considered field factors were represented in the climatic factors of daily maximum and minimum temperatures (°C), soil temperatures at 5 cm depth (°C), and the prevailed natural enemies with an estimation of phenolic contents (free and bound phenols) in the selected wheat cultivars. To investigate the efficiency of all considered factors together and each factor separately on the population fluctuation of onion thrips, Thrips tabaci Lindeman and aphid species (Mayzus persicae Sulz., Brivecoryne brassicae Linnaeus, and Rhopalosiphum padi Linnaeus) on the selected wheat cultivars under drought and field conditions in relation to the yields of cultivars. The mean numbers of thrips were higher than aphid species on most of the selected cultivars during the two studies seasons. The individuals of both insect pests were observed in the 15th of February, 2015 for the 1st season, while in the second season the infestations started in the 15th of January, 2016 on all of cultivars. The 1st season peaks by aphids were showed from the 15th of March to the 30th of April, 2016 on all cultivars, while two peaks of thrips population were observed on Sahel 1 and Seds 4, and three outbreaks on the rest of cultivars. The number of the peaks during the 2nd season by aphids and thrips were reached to two peaks for each pest during the 28th of April and the 15th of March, 2016. The efficiency (R2 x100) of all experimental considered factors were (72.98, 64.07, and 80.03%; respectively for aphids, thrips, and pests total grand). The considered factors were regulated the populations of pests during the studied seasons according to their efficiency in the following order for aphids: the natural enemies, the min. temperatures, the soil minimum temperatures were mainly participated with (20.847, 15.003, and 11.265 out of 72.98%; respectively for on all the cultivars), while The bound phenols were the least efficient factor (0.994 out of 72.98%). For thrips and the pests grand totals, the soil minimum temperature, the maximum temperature, and the minimum temperature were affected the population density by (22.099, 27.757; 12.914, 20.473; and 9.053, 11.377 out of 64.07 and 77.76%; respectively for thrips and the grand totals of pests) and the least efficient factor for thrips was free phenol contents (0.655 out of 77.76%, r= -1.082), and for the grand totals of pests were the natural enemies (0.169 out of 77.76%, r= 0.633). In both seasons, the greatest yield were obtained from from Giza 186 (178.33 and162.39 GY/10 plants; respectively in the 1st and the 2nd season). Meanwhile, the lowest one was recorded from Gemaza 9 (81.66 and 95.13 GY/10 plants; respectively in the 1st and the 2nd season).