Dynamics of Source Strength, Seed Yield and C:N Ratio in Cuphea Spp.
Abdullah Jaradat, USDA-Agricultural Research Service, 803 Iowa Ave., Morris, MN 56267 and Jana Rinke, ARS-USDA, 803 Iowa Ave, Morris, MN 56267.
Dynamics of flowering and capsule formation (scaled as number of flowers or capsules per unit biomass), C:N ratio and seed yield per plant of an indeterminate Cuphea spp. germplasm line (C. lanceolata x C. viscosissima) were impacted by defoliation at 100, 200 or 300 growing degree days (GDD1, 2, and 3, respectively) after flower initiation. Temporal patterns of flowering and capsule set were largely time-dependent and highly auto-correlated, with the significant autoregressive parameters of number of flowers (>0.76) and number of capsules (>0.74) being associated with large 95% confidence intervals (0.55 to 0.97 and 0.52 to 0.94, respectively).Stronger coupling was found between flowers and capsules (r= 0.82 for the control to 0.93 for GDD3; p<0.001) as the defoliation time was delayed. Reproductive failure (i.e, percent aborted flowers) was positively impacted by scaled capsules and its interaction with scaled flowers, and negatively by scaled flowers; it decreased from 43% (control) to 25% (GDD3) with larger model fit in defoliated (R**2 = 86-92) as compared with control (R**2=65) plants. Plant dry weight, single seed weight, and number of seeds per plant exhibited non-linear relationships with, and explained 96% of variation, in C:N ratio in the seed; these yield components, in addition to capsules and total seed weight per plant, were negatively correlated with C:N ratio. Removal of the upper 25% of foliage at successive GDDs resulted in a gradual and significant decrease in C:N ratio of seed (from 18:1 to 15:1) and a gradual and significant increase in seed weight per plant (from 1.07 to 1.82 g) as compared with the control.