RESPIRATION AND GERMINATION RATES OF TOMATO SEEDS AT SUBOPTIMAL TEMPERATURES AND REDUCED WATER POTENTIALS

Suboptimal temperature (T) affects germination rates (reciprocal of ti me to radicle emergence) on a thermal time basis; that is, the Tin exc ess of a base or minimum temperature multiplied by the time to a given per cent germination (t(g)) is a constant. Respiration rates are also sensitive to T, and proportional relationships are often found betwee n respiration rates and germination rates, Reduced water potential (ps i) delays seed germination on a hydrotime basis (i.e. the psi in exces s of a base water potential multiplied by t(g) is a constant), It was tested whether respiration rates prior to radicle emergence vary in pr oportion to T and psi as expected from the thermal and hydrotime model s, Respiration rates (CO2 evolution) of cold-tolerant, rapidly germina ting (PI 341988) and cold-sensitive, more slowly germinating (T5) toma to (Lycopersicon esculentum Mill.) seeds were evaluated over a range o f T and psi conditions, For both genotypes, respiration rates until th e beginning of radicle emergence were related to T on a thermal time b asis and increased approximately linearly with psi above -2.0 MPa, con sistent with the hydrotime model. Respiration rates were uniquely rela ted to germination rates, regardless of whether germination timing was affected by T, psi, or genotype, However, germination timing was unaf fected when respiration rates were manipulated by varying O-2 partial pressure. Thus, while both germination and respiration rates vary with T and psi consistent with thermal and hydrotime models of biological time, respiration rates per se were not the limiting factor in germina tion timing of tomato seeds.