Photosynthesis of Peanut Canopies as Affected by Leafspot and Artificial Defoliation¹

Abstract

Cercospora sp. leafspot and defoliating arthropods are major pests which reduce the yield of peanuts (Arachis hypogaea L.) in the southeastern United States by decreasing the amount and effectiveness of photosynthetic surfaces. Nevertheless, in the past, yield reductions have been empirically predicted from season‐end yields without considering the intermediate effects of leafspot or defoliation on canopy photosynthesis. Information on short and long term responses of crop growth processes to these pests is vital to the development of croppest management models which dynamically simulate crop and insect interaction. Our objective was to determine canopy photosynthesis and characteristics of peanut foliage layers in response to leafspot, defoliation, and combinations of disease and defoliation. Measurements from a field experiment included canopy C exchange rate (CER), photosynthetic uptake of 14CO2, leaf area, and light interception by leaves in three canopy layers. The upper 42% of the canopy leaf area intercepted 74% of the light and fixed 63% of the total 14CO2 taken up by intact canopies. Removal of 25% of the total leaf area, primarily from the upper half of the canopy, reduced 14CO2 uptake by 30% and canopy CER by 35%. In 1977, severe leafspot damage reduced leaf area index (LAI) by 80%, 14CO2 uptake by 85%, and canopy CER by 93%. Canopy CER values measured in 1978 were reduced 35 and 65% for medium and high leafspot damage treatments, respectively. Photosynthesis of diseased canopies was reduced not only by loss of leaves which abscissed as a result of infection, but also because diseased leaves which remained on the plants were less efficient in fixing CO2. Modeling the effects of insect defoliation and leafspot on peanut plant growth will require the fraction of LAI lost relative to LAI of 3 or 4, as well as the location and photosynthetic rate of the leaves remaining after insect defoliation or disease.

Effects of leaf blast on photosynthesis of rice 2. Canopy photosynthesis

“…Cercospora sp. leafspot in peanuts (Boote et al, 1980) and Verticillium dahliae in potato (Bowden and Rouse, 1991 )). The contribution of both components to the overall reduction varies and is related to the relative extent of diseased and dead leaf area.…”

Gas Exchange and Emission of Chlorophyll Fluorescence during the Monocycle of Rust, Angular Leaf Spot and Anthracnose on Bean Leaves as a Function of their Trophic Characteristics

“…The disease process that is a result of the interaction between a pathogen and its host leads to changes in several physiological processes of the host plant, including dark respiration, photosynthesis, translocation of water and nutrients, transpiration, and regulation of growth (Lucas, 1998). Fungal infection generally reduces the photosynthetic rate by decreasing functional leaf area and reducing the photosynthetic efficiency of the remaining green leaf area (Livne, 1964; Raggi, 1978; Boote et al., 1980; Bastiaans, 1991; Shtienberg, 1992; Bassanezi et al., 1997, 2000; 2001). Dark respiration of leaves usually rises after infection (Daly et al., 1961; Raggi, 1978; Owera et al., 1981; Martin, 1986; Bassanezi et al., 2001) in consequence of increased metabolic activity of cells of the diseased leaf (Lucas, 1998).…”

Leaf Gas Exchange and Chlorophyll a Fluorescence Imaging of Rice Leaves Infected with Monographella albescens

“…Understanding the physiological changes of a pathogen's host during the infection process can help to predict the effects of diseases on crop growth and yield (8,10). Photosynthesis, a major driver of crop yield, is the key physiological process affected by foliar pathogens (6,7,12,13,33).…”