Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes II. GERMINATION AT REDUCED WATER POTENTIAL

TLDR: It appears that the primary effect of priming was to shorten the time required for final endosperm weakening to occur, as priming increased GR even in cut seeds, and priming effects on the embryo may control the rate of endOSperm weakening.

Abstract: Seed germination rates (GR = inverse of time to germination) are sensitive to genetic, environmental, and physiological factors. We have compared the GR of tomato (Lycopersicon esculentum Mill.) seeds of cultivar T5 to those of rapidly germinating L. esculentum genotypes PI 341988 and PI 120256 over a range of water potential ( were also assessed. Germination time-courses at different 0's were analysed according to a model that identified a base, or minimum, \j> allowing germination of a specific percentage (g) of the seed population (ifib(g)), and a 'hydrotime constant' (9H) indicating the rate of progress toward germination per MPa.h. The distribution of if>b(g) determined by probit analysis was characterized by a mean base b) and the standard deviation in b among seeds ( . A normalized time-scale for comparing germination responses to reduced ij> is introduced. The time to germination at any tp (t g(tfi)) can be normalized to be equivalent to that observed in water (/g(0)) according to the equation fg(0) = (l -^(ip/Ms)))^^)- PI 341988 seeds were more tolerant of reduced > b(g), but did not lower the minimum b between intact and cut seeds incubated at high 0 was much less («0-l MPa), indicating that at the time of radicle protrusion, the endosperm had weakened to the point where it constituted only a small mechanical barrier. In the intact seed, endosperm weakening and the downward adjustment in embryo ifib ceased at </i < — 0-6 MPa, while the reduction in 8H associated with priming proceeded down to at least —1-2 MPa. Based on these data and on the pressure required to push the embryos from the seeds at various times after imbibition, it appears that the primary effect of priming was to shorten the time required for final endosperm weakening to occur. However, as priming increased GR even in cut seeds, priming effects on the embryo may control the rate of endosperm weakening.