Abstract:
Soursop (Annona muricata L.) cultivation faces several challenges, including the
protogynous nature of its flowers, limited pollinator presence, and a prolonged, highly
variable initial quiescent period during fruit development. This study aimed to assess
the effects of plant growth regulators (PGRs) on reducing the initial quiescent period,
enhancing fruit growth, and increasing fruit set in soursop. Hand-pollinated flowers
were treated with various concentrations of naphthaleneacetic Acid (NAA) alone and
in combination with gibberellic Acid (GA3). Treatments included NAA
concentrations of 1000, 2000, 3000, 4000 ppm and 5000 ppm, as well as combined
applications of NAA 4000 ppm + GA3 1000 ppm and NAA 5000 ppm + GA3 1000
ppm. Each treatment was replicated across three blocks of 10 samples, with a total of
24 trees being used in this study. Hand pollination flowers without PGR applications
were considered as the control. Weekly measurements of fruit length and
circumference were recorded, with the quiescent period considered broken upon rapid
increases in these metrics. The data were analyzed using a repeated mixed model and
a Poisson regression, with the number of weeks until the quiescent period was broken
as the dependent variable. The results indicated that NAA concentrations of 3000 ppm
significantly reduced the quiescent period, achieving the shortest median time to
success. Higher NAA concentrations did not consistently yield better results, and the
addition of GA3 showed no significant improvement (p<0.05) over the use of NAA
alone. All PGRs applications recorded more than 90% fruit set compared to the non
PGR applied control, which only achieved 63% success. Application of 3000 ppm
NAA concentration demonstrated strong potential for practical application, offering
the shortest quiescent period (5 weeks), greater success and the lowest fruit drop rates.
Furthermore, the findings highlighted the benefits of using NAA at optimal
concentrations to enhance soursop cultivation. This approach offers promising
methods to improve fruit set and reduce the quiescent period of soursop.
