Mesure journaliére sur cycle végétatif complet des échanges gazeux: photosynthése, transpiration et respiration nocturne ďune culture de Maïs conduite sur colonnes de sol

Daily measurement of gas exchanges during a complete growth cycle: photosynthesis, transpiration and night respiration in a soil culture of maize. During a complete growth cycle, photosynthesis (P), night-respiration (R) and transpiration (T) have been measured daily for maize (Zea mays L. cv. INRA F7 × F2) in a self-regulating growth chamber. P and T varied according to three different kinetics. During the growing period there was a fast and concomitant variation of both P and T, which could be filled to a power function of time. During the fructification period we observed a linear decrease of P and T. Finally, during the senescence period P decreased to zero, whereas T kept a value higher than the evaporation of the naked soil. In the first two periods, the P/T ratio decreased as leaves aged. From this we could deduce that a slow increase of stomatal resistance (RS) and mesophyll resistance (RM) took place. R increased until the panicle appeared; it remained constant during fructification and then it decreased with senescence. Each nitrogen supply induced a transient increase of R. Finally, a water stress led to a greater decrease of P than of R, but the after effect of water stress disappeared a day later. These results were compared with those obtained in hydroponic conditions.     

Evaluation of buffalograss germplasm for resistance to Blissus occiduus (Hemiptera: Lygaeidae)

Blissus occiduus Barber has emerged as an important insect pest of buffalograss, Buchlo? dactyloides (Nuttall) Engelmann, in Nebraska. This research evaluated selected buffalograss germplasm for resistance to B. occiduus. Eleven buffalograss selections were screened for chinch bug resistance in three greenhouse studies and two field evaluations. Based on chinch bug damage, NE91-118, 'Tatanka', 'Bonnie Brae', and 'Cody' were rated highly to moderately resistant. These four buffalograsses exhibited minimal damage, even though all were heavily infested with chinch bugs. NE84-45-3 and '378' were highly susceptible to B. occiduus. Field evaluations confirmed chinch bug resistance ratings under field conditions. NE91-118 displayed high levels of resistance in the field screening evaluations, whereas Cody and Tatanka showed moderate levels of resistance, and 378 was highly susceptible.     

Characterization of oxidative enzyme changes in buffalograsses challenged by Blissus occiduus

This research investigated the role of oxidative enzymes in the defense response of buffalograss, Buchlo? dactyloides (Nuttall) Engelmann, to Blissus occiduus Barber. Changes in catalase and peroxidase activity were observed in both resistant and susceptible buffalograsses in response to chinch bug feeding. Susceptible plants were shown to have a lower level of catalase activity compared with their respective control plants. By contrast, catalase activities of resistant plants were similar between infested and control buffalograsses throughout the study. Resistant plants had higher levels of peroxidase activity compared with their control plants, whereas peroxidase activities for control and infested susceptible plants remained at similar levels or were slightly lower for infested plants. These findings suggest that chinch bug feeding leads to a loss in catalase activity in susceptible buffalograsses. In contrast, resistant buffalograsses may be able to tolerate chinch bug feeding by increasing their peroxidase activity. Polyphenol oxidase activities were similar between control and infested plants for the buffalograsses evaluated. Among the enzymes examined, no differences in isozyme profiles for peroxidase and polyphenol oxidase were detected between control and infested 378, NE91-118, Cody, and Tatanka plants. Gels stained for catalase identified differences in the isozyme profiles of infested and uninfested 378 plants; however, infested and control NE91-118, Tatanka, and Cody plants has similar isozyme profiles. No differences in protein profiles were observed between chinch buginfested 378, NE91-118, Cody, and Tatanka plants and their respective uninfested controls.