|Pennypacker B W, - THE PENNA STATE UNIV|
|Knievel D P, - THE PENNA STATE UNIV|
|Risius M L, - THE PENNA STATE UNIV|
|Leath K T,|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 1994
Publication Date: N/A
Interpretive Summary: Some alfalfa plants are resistant to the wilt disease caused by the fungal pathogen, Verticillium albo-atrum, whereas other plants die once they are infected. The plant's ability to maintain photosynthesis and produce carbohydrates following infection is suspected of being a key determinant as to whether the plant is resistant or not. Infected, resistant, genetically identical alfalfa plants were grown under low, moderate and normal light conditions to study further this relationship between photosynthesis and resistance. At the lowest light level, 40% of normal and inadequate to support maximum photosynthesis, normally resistant plants responded as if they were susceptible. The increased susceptibility was directly related to the impaired photosynthetic capability of the normally resistant plants when grown in insufficient light. This research provides a key piece of the puzzle as to why some plants resist disease while others succumb.
Technical Abstract: Resistance of an alfalfa clone to Verticillium albo-atrum was attenuated by manipulating photosynthetic photon flux density (PPFD). Effects of PPFD and V. albo-atrum on dark respiration, in vivo ribulose 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activity, in vitro total Rubisco activity, quantity of Rubisco, molar activity of Rubisco, and ribulose bisphosphate (RuBP) regeneration rate were examine in a factorial experiment with pathogen (inoculated or noninoculated) and PPFD (40, 70, and 100% PPFD) as the treatments. Pathogen x PPFD interactions were detected in dark respiration, total protein, and amount of Rubisco. Dark respiration was suppressed by V. albo-atrum under 40% PPFD, increased under 70% PPFD, and unaffected by the pathogen under 100% PPFD. Total protein and Rubisco were reduced in inoculated plants only under 40% PPFD. In vitro total Rubisco activity was increased and regeneration rate of RuBP was reduced in all inoculated plants. The photosynthetic properties of the inoculated, resistant plants under 40% PPFD mimicked those reported for susceptible plants, but only dark respiration and amount of Rubisco were reduced by the presence of V. albo-atrum; the other properties were reduced by the PPFD treatment. The increase in in vitro total Rubisco activity and decrease in RuBP regeneration rate in inoculated, resistant alfalfa suggest that photosynthetic acclimation may be optimizing carbon assimilation in alfalfa resistant to V. albo-atrum.