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Aspects of the nitrogen relations of the sorghum-Striga hermonthica host-parasite association
Başlık:
Aspects of the nitrogen relations of the sorghum-Striga hermonthica host-parasite association
Yazar:
Cechin, Ines, author.
ISBN:
9780438083592
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (221 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Özet:
Striga hermonthica is an angiosperm root parasite native to the semi-arid tropics. It is a major threat to cereal cultivation in semi-arid parts of Africa, where it is a major problem for subsistence farmers in particular. In this thesis the influence of nitrogen on aspects of the sorghum-S. hermonthica association have been examined. S. hermonthica has a marked effect on its sorghum host. It reduced the growth and also affected its allometry. Grain yield and stem dry weight were the most severely affected. Infected plants a had higher root/shoot ratio compared to uninfected plants which arises as a result of both inhibition of shoot growth and stimulation of root growth. In addition, infected plants had lower light-saturated rates of photosynthesis. The influence of S. hermonthica on these variables is dependent on the concentration of nitrogen supplied. Increased nitrogen supply increased the biomass and photosynthesis of uninfected plants and resulted in an alleviation of the deleterious effects of S. hermonthica. At the lowest nitrogen concentration the effect of S. hermonthica was large compared to a negligible effect at the highest nitrogen concentration. Moreover, increased nitrogen supply also resulted in lower numbers and biomass of S. hermonthica per host. S. hermonthica seed germination was negatively correlated with nitrogen supply. The nitrogen effect on S. hermonthica germination is exerted via processes which occur in sorghum roots before the germination stimulant is exuded. Following germination nitrogen also influences S. hermonthica attachment and early growth. S. hermonthica is highly dependent on its host for carbon. However, at high nitrogen supply the proportion of heterotrophic carbon in S. hermonthica leaves is lower concurrent with a stimulation of photosynthesis. This partially explains the smaller effect on its host at high nitrogen supply. S. hermonthica-infected sorghum plants had lower light-saturated rates of photosynthesis These can not be accounted for by lower rates of stomatal conductance. The relationship between photosynthesis and intercellular CO2 concentration demonstrated that the parasite affects photochemical rather than biochemical limitations. Modulated chlorophyll fluorescence analysis suggested that infected plants have a lower quantum efficiency of excitation capture by PSII reaction centres and a lower quantum efficiency of PSII electron transport. In addition to its influence on growth and photosynthesis, S. hermonthica also affected the carbohydrate status of its sorghum host. A lower starch content in infected plants was observed at the end of dark period. This suggests that a greater starch mobilization is required to supply carbon to the extra sink formed by S. hermonthica. S. hermonthica influences the growth and allometry of rice in a similar manner to that of sorghum. However, the higher nitrogen concentration did not alleviate the effects of S. hermonthica to the same degree that it did on sorghum. In addition, the photosynthetic dysfunction seen in rice is attributed to both biochemical and photochemical limitations.
Notlar:
School code: 1543
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(686881.1) | 686881-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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