Growth and yield comparisons of Pix® Plus and additional Bacillus cereus treated cotton

Abstract

Pix® Plus, a plant growth regulator (PGR) applied to cotton (Gossypium hirsutum L.), is a combination of mepiquat chloride (MC) and Bacillus cereus (BC). Mepiquat chloride is a gibberellic acid (GA) synthesis inhibitor, which is a natural plant hormone that promotes shoot cell elongation. Therefore, MC is commonly applied to control vegetative growth. Although MC has been reported to increase yields, responses have been erratic. Reduced vegetative growth may allow photoassimilates to be reallocated to plant reproductive structures, increasing yield potential. Reduced shoot growth results in decreased plant height, which can potentially reduce total sympodial node production resulting in fewer total fruiting sites. The bacterium, BC, in a symbiotic relationship with cotton, purportedly enhances plant growth. Thus, the combination of MC and BC allows for the control of excessive vegetative growth while potentially shifting allocation of photoassimilate and promoting reproductive growth. Foliar BC rates, application timing, and the most effective MC to BC combinations for use in cotton have not been fully explored. Field experiments were conducted in 1999 and 2000 at the Texas Agricultural Experiment Station in Burleson County, Texas to assess the benefits of additional BC applications to Pix® Plus treated cotton. Experimental design was a six treatment Latin square with five experimental treatments and an untreated check (UTC). All five treatments received 0.58 L ha⁻¹ Pix® Plus at match-head square (MHS) and early bloom (EB) as the area standard treatment (AS), while three treatments received an additional 70.1 g ha⁻¹ application of BC at pin-head square (PHS), EB, or three weeks after EB (EB+3). The remaining treatment received 70.1 g ha⁻¹ BC at all three timings (BCX3). Mid-season monitoring measurements supported typical MC results. Fruit counts at EB were higher in the PHS treatment than all others. Plant height at harvest was reduced in all Pix® Plus treatments, while nodes at harvest were unaffected, resulting in a reduced height to node ratio (HNR). Box mapping at maturity revealed no differences among boll weights or boll distribution. In 1999, there were no differences in yield although additional BC applications in 2000 showed some differences in seedcotton and lint yield.