Two types of fluorimeter (inductíon and modulated) were employed to compare the intrinsic photosystem 2 efSciency of sun-exposed and shaded flag leaves of two cultivars (ICSV112 and Aralba) of sorghum, in the irrigated and unirrígated fleld plots at Monterotondo, Rome. Generally there was a good correlation between instruments, but for the irrigated sun adapted leaves of both cultivars much larger ratios were recorded with the modulated fluorimeter than with the inductíon one. This discrepancy was attributed to an insufficient flash intensity in the inductíon systém when measuring the healthy leaves adapted to a high irradiance.
Time course of symbiotic N2-fixing and photosynthetic activities during vegetative growth from 30 d after plantation until pod set was measured in the CB5 and 7964 cowpea [Vigna unguiculata (L.) Walp.] genotypes of contrasting senescence traits. At emergence, seedlings were inoculated with a "non-cowpea miscellany" Rhizobium strain generally used to inoculate Cicer arietinum. Maximum N2-fixing activity occurred in inoculated CB5 and 7964 plants about 54 and 68 d after plantation, respectively. A similar temporal shift of maximum was found for net photosynthetic rate
(PN), confirming a good coordination between the two processes. A higher PN was found from the first measurements in inoculated plants of both genotypes as compared with uninoculated plants. Apparently, the maximum activity of both N2-fixation and PN was timed to occur at a particular stage of plant ontogeny correlating the high N supply with the high N demand by the plant. Rhizobium inoculation did not significantly affect partitioning coefficients of biomass to various plant organs but extended leaf longevity by about 10 d in the CB5 genotype, retarding thus the monocarpic senescence. and D. Lippi ... [et al.].