Cotton gin trash compost in the substrate reduces the daminozide spray dose needed to produce compact potted chrysanthemum

Abstract

Research was conducted to evaluate cotton gin trash compost (CGC) as a peat substitute in the growth medium of compact potted chrysanthemum, and its possible interaction with the plant growth retardant butanedioic acid mono-(2,2- dimethylhydrazide) (daminozide) applied to control plant size. Rooted terminal cuttings of Dendranthema grandiflora Tzvelev. var. Yoko Ono were potted in an 1 peat: 1 perlite (by volume) medium or in an 1 CGC: 1 peat: 2 perlite (by volume) medium and their foliage was sprayed three times with an aqueous solution of 0, 2000, 2500, 3000 or 3500mgl−1 daminozide. The replacement of half of the peat amount in the growth medium with CGC had a restrictive effect on shoot elongation, retarding mainly the internodal length, effect similar to that induced by daminozide. Plants grown in the CGC medium and not treated with daminozide had similar shoot lengths as plants in the peat-perlite medium sprayed with 2000 or 2500mgl−1 daminozide. The combination of CGC with the lowest daminozide concentration used (2000mgl−1) induced shoot growth retardation similar to that induced by the highest concentrations (3000–3500mgl−1) of daminozide in the peat-perlite medium. Leaf size was reduced by CGC as by the higher doses of daminozide, while flower head size was not affected. Both, daminozide and CGC, induced an acceleration of flowering, but the final flower head number was not affected. CGC decreased shoot, flower head and peduncle dry weights and increased root dry weight. At planting day, CGC medium had higher pH, EC, bulk density and total solids and lower total porosity and EAW (easily available water) compared to peat-perlite medium; it also held less water in saturation and drained faster. At the end of the experiment the two media had similar pH and EC values. Substitution of 50% peat with CGC in the commonly used medium for potted chrysanthemum commercial cultivation resulted in a reduction of at least 33% of the dose of daminozide necessary to meet the needs of the market for compact plants, with multiple economic and environmental benefits.