Screening of Genotypes of Brassica juncea L. for Leaf Conductance under Field Conditions

Twenty-three genotypes of Indian mustard were studied for leafconductance (K₁) at the floral bud initiation stage under non-stressconditions. The comparison of leaf conductance and of severalother measurements in the standard cultivar ‘Prakash’demonstrated that a screening procedure could be developed forleaf conductance prior to the flowering stage of mustard grownin the field. Errors due to short term environmental fluctuationsand to ontogenetic drift in conductance can be reduced if themeasurements are made on both the ad- and abaxial surfaces ofthe uppermost expanded leaf between 1200 h and 1400 h on cleardays. Irradiance levels can be neglected once a value of photosyntheticallyactive radiation (PAR) of about 1000 µE m^–2 s^–1at the adaxial surface or of 1200 µE m^–2 s^–1at the crop canopy has been reached. The water status of theplants is of no importance as long as the plants are not underundue stress. The different genotypes showed a genetic variabilityof 243% in leaf conductance.