Publication Date
1993
Description
Alfalfn (Medicago saliva L.) clones, susceptible and resistant to Verticillium albo-atrum (Van), were systematically infected with Vaa via stubble inoculation with conidial suspensions. Progress of infection and anatomical host responses was monitored by sequential sampling, sectioning, staining and examination with light microscopy. Effect of infection on photosynthesis was assessed in vivo by measuring net photosynthesis and activity of ribulose 1, 5-biphosphate carboxylaseoxygenase (rubisco) via a CO2 drawdown curve. hr vitro activity of rubisco was determined by protein extraction and uptake of radioactive CO2. Susceptible and resistant clones exhibited leaflet chlorosis and abscission. Also, the pathogen produced spores that germinated within xylem vessels. All these activities occurred faster and were more severe in susceptible than in resistant clones. In both clonal types, xylem vessel walls were coated with suberin and lignin; pit chambers and vessel elements were plugged with pectins and gums; and vessel element differentiation was disrupted. Enlargement of new vessel elements was inhibited, resulting in nnrrow-lumened vessels. Vessel element disintegration occurred about 2 weeks after inoculation in the susceptible clone but not until 6 weeks in a resistant clone. One resistant clone also exhibited a containment response consisting of hypertrophied xylem parenchyma cells that encircled and crushed infected vessels, preventing further development of Vaa. In resistant clones, hyphae were often coated with a thick material that gave a positive test for lignin and suberin, Such an encasement formation resembled a "lignituber", and appeared to be part of the defence response. Vaa significantly reduced net photosynthesis, and in vivo and in vitro rubisco activity in susceptible but not resistant clones. The reduced rubisco activity caused the reduced net photosynthesis in the susceptible clone.
Citation
Pennypacker, B W.; Leath, K T.; Knievel, D P.; and Pell, E J., "Resistance Versus Susceptibility to Verticillium albo-atrum in Alfalfa" (2024). IGC Proceedings (1993-2023). 24.
https://uknowledge.uky.edu/igc/1993/session22/24
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Resistance Versus Susceptibility to Verticillium albo-atrum in Alfalfa
Alfalfn (Medicago saliva L.) clones, susceptible and resistant to Verticillium albo-atrum (Van), were systematically infected with Vaa via stubble inoculation with conidial suspensions. Progress of infection and anatomical host responses was monitored by sequential sampling, sectioning, staining and examination with light microscopy. Effect of infection on photosynthesis was assessed in vivo by measuring net photosynthesis and activity of ribulose 1, 5-biphosphate carboxylaseoxygenase (rubisco) via a CO2 drawdown curve. hr vitro activity of rubisco was determined by protein extraction and uptake of radioactive CO2. Susceptible and resistant clones exhibited leaflet chlorosis and abscission. Also, the pathogen produced spores that germinated within xylem vessels. All these activities occurred faster and were more severe in susceptible than in resistant clones. In both clonal types, xylem vessel walls were coated with suberin and lignin; pit chambers and vessel elements were plugged with pectins and gums; and vessel element differentiation was disrupted. Enlargement of new vessel elements was inhibited, resulting in nnrrow-lumened vessels. Vessel element disintegration occurred about 2 weeks after inoculation in the susceptible clone but not until 6 weeks in a resistant clone. One resistant clone also exhibited a containment response consisting of hypertrophied xylem parenchyma cells that encircled and crushed infected vessels, preventing further development of Vaa. In resistant clones, hyphae were often coated with a thick material that gave a positive test for lignin and suberin, Such an encasement formation resembled a "lignituber", and appeared to be part of the defence response. Vaa significantly reduced net photosynthesis, and in vivo and in vitro rubisco activity in susceptible but not resistant clones. The reduced rubisco activity caused the reduced net photosynthesis in the susceptible clone.
