ASSESSMENT OF RESISTANCE TO PINK STEM BORER AND APHID INFESTATION IN SWEET SORGHUM CULTIVARS AND THEIR PRODUCTIVITY AND TECHNOLOGICAL TRAITS UNDER FOUR SOWING DATES

Two field trials were conducted at El-Fayoum Governorate, Tamia destrict (29o17N, 30o53E), Egypt, during summer 2017 and 2018 seasons, to evaluate the susceptibility to two dangerous insect pests i.e. pink stem borer (Sesamia cretica) and corn leaf aphid (Rhopalosiphum maidis) under natural infestation, the productivity, quality of ten sorghum cultivars (Brands, Dale, Honey, Leoti, Planter, Rex, Rio, Tracy, Umbrella and Williams) sown under four sowing dates (Mid. April, May, June and July). The results of the separate and combined seasons indicated that all noticeable signs of damage parameters of pink stem borer and corn leaf aphid significantly increased gradually with delaying sorghum sowing. Sowing in mid June or July suffered more damage to both insects as compared with early sowing. Regarding the noticeable damage signs. It significantly differed among the ten sweet sorghum cultivars, where, Rio, Dale and Williams cultivars recorded the least infestation which gave evidence that those cultivars were relatively tolerant to both insects, while, Honey and Umbrella cultivars recorded the highest infestation features. Quality traits (TSS, Sucrose% and reducing sugars) insignificantly differed among the four sowing dates and cultivars. Juice Extraction Percentage (JEP), glucose ratio (GR) and juice purity significantly differed among the four sowing dates. The values of JEP and juice purity decreased gradually as sowing date delayed, while, GR recorded the lowest value on May sowing as compared with other three sowing dates. On the contrary, Syrup Extraction Percentage (SEP), Total Fermentable Sugars (TFS) and Fiber % were insignificantly differed among the four sowing dates. Great variation has been detected for all processing parameters among the tested cultivars except TFS%. The results also showed that all productivity traits were significantly decreased as sowing date delayed to reach its minimum at July sowing. Productivity clarified that average stripped stalk wt., stripped stalk, juice, syrup and ethanol yields significantly differed among the tested cultivars (except forage yield). Rio cultivar yielded the highest productivity traits, while, Honey cultivar exhibited the lowest ones. The variation observed among the tested sorghum cultivars for all studies traits were markedly related to the tolerance and susceptibility of used the tested cultivars to pink stem borer and corn leaf aphids which measure by many constant parameters as discussed previously. In general, Rio, Dale and Williams sorghum cultivars sown on mid April sowing dates exhibited the higher productivity and quality traits and the lower damage signs or to some extend characterized as relatively tolerance to pink borer and corn leaf aphid infestation.