Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Abstract

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow‐growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow‐growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow‐growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn‐over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.

Changes in chemical composition related to fungal infection and induced resistance in carnation and radish investigated by pyrolysis mass spectrometry

“…Significant differences in disease incidence between bacterized and non-bacterized plants were found from 17 days after inoculation onwards (Steijl et al, in preparation). The results are in agreement with those of a large number of independent experiments performed in our laboratory [25,26,30,31 ].…”

“…Healthy plants As indicated by previous PyMS analysis, slow-growing, resistant radish cultivars contained more cell wall material in the leaves but less in the roots when compared to faster-growing, more susceptible ones [25 ]. The within-variation of the group of root samples of untreated plants of cultivar SaxaiNova was not analysed separately.…”

“…raphani has so far eluded clarification. Resistance appears to be of a quantitative nature because cultivars with a range of resistance levels are known [25 ]. Resistance is associated with restricted relative growth rate [25 ], suggestive of a relationship between limited infection and reduced cell expansion potential.…”

Influence of cucumber mosaic virus infection on the growth response of Portulaca oleracea (purslane) and Stellaria media (chickweed) to nitrogen availability

“…These results suggest a negative relationship between  and plant tolerance to virus infection, as recently hypothesized to explain the difference in tolerance to fungi between genotypes of radish (Hoffland et al, 1996). A higher tolerance to virus for species and genotypes with low  could be the consequence of lower production and transport of photosynthates, inhibiting the multiplication and translocation of the virus.…”

Biotic and abiotic consequences of differences in leaf structure

“…One can also compare different genotypes under the same conditions to estimate whether the cost of defence is significant. Hoffland et al (1996) found that radish cultivars that were more protected against a fungus had to bear significant costs of more cell wall in leaves (but less wall and more protein in roots). Darrow & Bowers (1997) found no apparent cost (as decreased growth rate) for more potent defences, namely the iridioid glycosides, in Plantago species that were better protected against lepidopteran insects.…”