Influence d'une hydromorphie modérée ou sévère sur la production de biomasse et les échanges gazeux de plants de peuplier euraméricain

Seedlings of three poplar clones (I-488, Rimini, and D-64) grown in plastic pots were submitted to three water regimes: (1) irrigated and well-drained control (T); (2) flooded with running water (Hr = 6 mg·L–1 of O2); and (3) flooded with stagnant water (Hs = 2 mg·L–1 of O2). A permanent water table was maintained at 5 cm above the soil surface for 2 months. The Hr and Hs treatments simulate the conditions of hydromorphic soils chosen for planting poplar in Tunisia where the attempts failed because of the lack of knowledge relating to the degree of tolerance of this species to waterlogging. Waterlogging significantly reduced growth (leaf initiation was inhibited, root decay and early leaf abscission occurred) and modified photosynthetic activity (stomatal closure and reduction of CO2 net assimilation rates). Intracellular CO2 values did not significantly differ between treatments (T, Hr, and Hs), indicating that both stomatal and nonstomatal limitations could be responsible for reducing CO2 net assimilation. However, the degree of disruption varied according to the treatment. Stagnant regime Hs had negative and irreversible effects on CO2 net assimilation rates and internal CO2 conductance for the full length of the treatments with stomatal closure after 40 days in Rimini and D-64 clones. The Hr treatment produced limited reactions; the development of hypertrophied lenticels and adventitious roots alleviated the negative effects of waterlogging with a distinct recuperation of net photosynthesis and CO2 internal conductance particularly for clone I-488. In the same way, the development of root adaptations was greater for I-488 than Rimini and D-64 clones, probably indicating a higher tolerance to flooding in the former clone. This approach could be used to select the clones intended for afforestation of the nonsaline hydromorphic areas.

Performance of Nine Apple Cultivars Grown with Six Fungicide Regimes

In 1993 a factorial experiment, involving nine apple cultivars on M.9 root-stock and six fungicide regimes, was established. The cultivars included `Delicious', `Golden Delicious', `York Imperial', `Redfree', `Freedom', `Liberty', NY 74828-12, NY 73334-35, and NY 74840-1. The fungicide treatments included earlyseason sprays of Bayleton or Dodine, separately or combined, and late-season sprays of Captan plus Benomyl alone or combined with early-season sprays of Bayleton plus Dodine. Non-sprayed trees served as a control. In 1995 leaves and fruits were evaluated for disease symptoms. Leaf spot (symptoms caused by black rot or alternaria leaf blotch) was most severe on `Redfree' and NY 73334-35, and least severe on `Delicious', `Golden Delicious', and `York'. By late summer NY 74828-12 had the most leaf abscission, whereas NY 74840-1, `Liberty', and `Delicious' lost the fewest leaves. Early-season fungicide sprays did not reduce early leaf abscission. Sooty blotch and fly speck, but not rots, were nearly eliminated by late-season applications of Captan plus Benomyl. Averaged over all fungicide treatments, more than half of the fruits from `Delicious', `Redfree', and NY 74828-12 were free of disease symptoms. Cultivars with <25% of the fruits without infection included `York', `Liberty', NY 74840-1 and NY 73334-35. `York' and `Redfree' had >25% of the fruits with rots, while all other cultivars had <9% fruits with rots. `Delicious' and NY 73334-35 had the fewest rotten fruits. Rots were not controlled by any fungicide treatment. `Liberty' and NY 73334-35 had the most flyspeck and `Redfree' had the least. `Liberty', NY 74840-1 and NY 73334-35 had the most sooty blotch and `Redfree' and NY 74828-12 had the least.

One-Sided Shift Trellising Addresses Harvest, Pest Management and Cultural Problems in Rubus

Static-V trellis increases raspberry yield, but fruiting shoots grow toward its center making harvest difficult. Shading causes early leaf abscission and it favors fungus diseases inside the V. Static training of floricanes and primocanes to opposite sides of a V trellis prevents neither harvest difficulty, nor primocane injury during harvest. In 1988-89 harvest difficulties were reduced by bloom-time shifting of floricanes on a V-trellis. Over 90% of fruiting shoots were oriented to the trellis ' exterior, but primocane shading and early leaf abscission continued. The 'bent fence' trellis was designed and tested in 1989. It shifts floricanes from horizontal orientation to an upright position on one side of a V-shaped trellis, thus retaining outward display of fruiting shoots and achieving unobstructed display of primocanes on the opposite side. Harvest efficiency, disease reduction, accurate deposition of pesticides, avoidance of solar injury (sun scald), and adaptation of mechanical pest control procedures are potentiated by this system. It also reduces impediments to studies of carbohydrate partitioning, photosynthetic efficiency, yield efficiency, and intraplant competition.