Adopting slight changes in agronomic practices to obtain bigger impacts on yield and yield quality: hybrid seed production of Platycodon Grandiflorus under tropical greenhouse conditions

Abstract

Recommendations given based on the performance of exotic crop species in the country of their origin has not given expected results under Sri Lankan conditions. Therefore, efforts have been taken to address major issues in export-oriented floricultural enterprises in Sri Lanka by adopting slight changes in agronomic practices targeting larger impacts on yield and yield quality leading to higher profits; more buyers and more exports. The present study is one such attempt of a series of studies conducted to find customized solutions for real problems specified by the crop species, management practices and environmental conditions. Platycodon grandiflorus is one of the major flower plant species cultivated in Sri Lanka for the exportation of F1 hybrid seeds. Comprehensive knowledge on floral biology (i.e. flowering behavior, time of anthesis, pollen viability, receptive stage and receptive time of the stigma) of parent lines is very important to produce F₁ hybrid seeds. However, unavailability of information regarding best receptive stage and receptive time of stigma is a limitation and it has led to reduced seed yield. The present experiment was conducted to study the effective receptive stage and receptive time of the day of Platycodon grandiflorus under tropical greenhouse conditions. Average yield obtained under the current pollination practice at the existing growth stage is 42 seeds/ pod. A combination of parent lines 2012/99 (Female) and 2026/99 (Male) was used to produce F₁ hybrid seeds of SPD 2008 variety. All female parent flowers were emasculated three days before pollination. Pollination treatment was started three days after emasculation and continued up to the seventh day. Artificial pollination was done either in the morning or in the afternoon on each day. The pollination days after emasculation in combination with the pollination time of the day were used as treatments. The ten treatments were replicated 15 times. Self-pollinating flowers were used as the control treatment. The research was conducted in Complete Randomized Design (CRD) and data were analyzed using Excel and Statistical Analytical Software (SAS) packages. The maximum seed yield of 81 per pod was recorded in the treatment of artificial pollination after five days of emasculation. Pollination between 5-7 days of emasculation had no significant difference in seed yield. The artificial pollination in the afternoon between 3-4 days of emasculation is significantly better than artificial pollination in the morning in terms of yield. There was an inverse relationship between seed weight and number of quality seeds per pod. Pollinating Platycodon grandiflorus flowers either in the morning or in the afternoon, 5‑7 days after emasculation gives nearly a two-times higher yield of quality seeds than that of contemporary pollination practices under tropical greenhouse conditions.