Gibberellic Acid Promotes Early Growth of Winter Wheat and Rye

Winter wheat (Triticum aestivum) planting in Nebraska is recommended for mid-September, but summer crops are often harvested in late September and early October. Also, weather may delay planting.

Gibberellin, first identified from a pathogenic fungus, is a family of natural growth promoters of which gibberellic acid (GA₃) may be the most active in stimulating stem elongation. GA₃ bioassays for stem growth were reported on common bean and winter wheat demonstrating differential sensitivity of cultivars and growth habits.

In this paper, between 2005 and 2011, field trials were conducted on winter wheat (Triticum aestivum L.) cultivars Goodstreak and Wesley and between 2007 and 2009, on winter rye (Secale cereale L.) cultivar Rymin at the University of Nebraska’s Panhandle Research & Extension Center, Scottsbluf. All plots in all trials were four rows with spacing of 30 cm. GA₃ was applied as Release LC, a 4% a.i. by weight formulation, i.e., 1 g GA₃/30mL, formulation (Valent BioScience Corp., Long Grove, IL). Release LC was serially diluted with water to achieve desired concentrations. In 2009 and 2010, 6-benzyl adenine (6BA) as MaxCel, a 1.9% a.i. by weight formulation (Valent Bioscience) was added to GA₃. For seed dip treatments used in all years, sufficient seed was weighed to plant 20 plots and treat with 1 L of water, GA3 solution, or GA3 + 6BA solution.

The results showed that heights in mid Nov showed a reduction with later planting. When planted about 1 Oct and 15 Oct, the delayed growth of Goodstreak, compared to planting two weeks earlier, was fully overcome by GA₃ at 250 ppm. For Wesley, 1000 ppm GA₃ was needed to nearly overcome later planting. Rymin rye gave an intermediate response between the two wheat cultivars. Spring and summer heights were not affected by GA₃. Spring biomass, yield and harvested seed germination showed no GA₃ effect. In later trials (planted in 2009 and 2010), the cytokinin 6-benzyl adenine (6BA) was added to GA₃ to stimulate tiller formation. In the 1^st year, 6BA at 2000 ppm depressed height, weight and yield without tiller promotion. Repeating the trial with lower rates (31 - 125 ppm 6BA) did not offer an additional advantage to GA₃.

This study demonstrated that GA₃ applied directly to seed would stimulate pre-winter seedling growth when seeds were planted from mid Sep to mid Oct. With GA₃ application, a two-week delay in planting could be overcome. This would result in the plant size and stand to be sufficient to resist wind-induced soil erosion during the winter and stabilize the field even though the field was planted later than recommended. This would also improve crop rotation when wheat is planted after a summer crop that is harvested in late September or early October. Furthermore, GA₃ gives an additional production practice in case of adverse weather resulting in delayed planting. Besides, considering its potential uses, applying GA₃ to seed can be considered as an “insurance policy” but its cost needs to be considered as well.

Article by Alexander D. Pavlista, et al, from USA.

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