Limitation to Photosynthesis in Pratylenchus penetrans‐ and Verticillium dahliae‐Infected Potato

Abstract

Mechanism(s) responsible for decrease in photosynthetic rates of potato (Solanum tuberosum L.) leaves infected by the fungus Verticillium dahliae (Kleb) and the nematode Pratylenchus penetrans (Cobb, Sher, Allen) have not been fully researched. Two growth chamber experiments were undertaken to determine the factors contributing to the decrease in CO2 exchange rates of young, fully expanded leaflets of potato (cv. Russet Burbank) plants grown in pots infested with P. penetrans and/or V. dahliae Treatments were P. penetrans‐infested soil, V. dahliae‐infested soil, soil infested with both the nematode and the fungus, and a noninfested control. Leaf CO2 response curves were measured at early (16 d after inoculation [DAI]) and late (42 DAI) stages of infection for all treatments at saturating light (1500 μmol m−2 s−1 of photosynthetically active radiation [PAR] using a portable photosynthesis system. Carbon dioxide exchange rates were also measured at 1000, 400, and 200 μmol m−2 s−1 PAR to determine leaf light response. At ambient CO2 concentration, concomitant infection by both pathogens significantly reduced C assimilation rate (A) and light use efficiency (μmoles CO2 fixed per μmol of light used), and increased the intercellular CO2 (Ci ) of these young leaves at 42 DAI, but not at 16 DAI. Infection by either pathogen alone had little or no effect on the leaf gas exchange parameters. Analysis of the curve relating A and Ci showed that either treatment alone did not change the initial slope of the curve at 16 DAI. A significant reduction in both the initial slope of A vs. Ci curves and A at Ci = 500 μmol mol−1 in the jointly infected plants were noticeable at 42 DAI indicating that nonstomatal effects could explain the reduction in C assimilation rate at this late stage of disease infection. Leaf patchiness might also be a contributing factor to this phenomena in the leaves of the jointly infected plants.

Photosynthetic response of pepper plants to wilt induced by Verticillium dahliae and soil water deficit

“…1e), which limited CO 2 supply to the chloroplast. Our results agree with previous studies which demonstrated that, following infection with V. dahliae, photosynthesis of potato and pepper was reduced early as a result of stomatal closure caused by drought stress in leaves (Bowden et al, 1990;Haverkort et al, 1990;Bowden and Rouse, 1991;Saeed et al, 1997Saeed et al, , 1999Goicoechea et al, 2001). By contrast, some authors have reported that other pathogenic mechanisms, apart from water stress, can play a significant role in either decreased photosynthesis or stomatal closure.…”

“…On the one hand, several authors have proposed that water stress induced by Verticillium infection is a crucial factor to explain the impaired leaf photosynthesis in diseased plants (Bowden et al, 1990;Haverkort et al, 1990;Bowden and Rouse, 1991;Lorenzini et al, 1997;Saeed et al, 1999). In most of these studies, the reduction in net photosynthesis was attributed to stomatal closure, which reduces the concentration of CO 2 within leaves.…”

Growth, yield and physiology of Verticillium-inoculated pepper plants treated with ATAD and composted sewage sludge

“…This result agrees with data reported for other plant species (Bowden et al 1990;Goicoechea et al 2001;Haverkort et al 1990;Lorenzini et al 1997;Pennypacker et al 1990;Sadras et al 2000;Saeed et al 1999). Vascular wilt pathogens decrease plant hydraulic conductance due to plugging of the xylem vessels by the fungus, which may lead to leaf water deficits (Adams et al 1987).…”

Multiplex Real-Time Quantitative PCR to Detect and Quantify Verticillium dahliae Colonization in Potato Lines that Differ in Response to Verticillium Wilt

“…Such plating methods were used to differentiate among cultivars and breeding lines in the selection for and study of resistance to PED (10,14,17,25-28, 45,62). Those assays were also employed to describe the epidemiology of the disease and colonization by the pathogen under various agricultural and environmental conditions (2)(3)(4)15,16,18,19,24,40,43,48,52,61). Expression of PED symptoms is greatly affected by environmental and agricultural conditions (e.g., weather during the growing season, irrigation frequency, and nitrogen fertilization), and selection of breeding lines based solely on symptoms is generally discouraged.…”

“…Additionally, ground rye seed infested with V. dahliae VCG4A isolate V18 were buried in the furrow with each tuber seed piece at planting (9 May 2005). Isolate V18 is a highly aggressive strain of V. dahliae that was isolated from severely affected potato plants in the same field and was used successfully in numerous studies of PED both in the field and in the greenhouse (2,3,(26)(27)(28)33,43,52).…”