Effect of Cercospora zeae-maydis infested maize residue on progress and spread of grey leaf spot of maize in central Uganda

The spread of grey leaf spot caused by Cercospora zeae‐maydis from infested maize residue on the soil surface and progress over time were studied under tropical conditions at two locations in central Uganda, Kabanyolo and Namulonge, using a susceptible local cultivar, LP16. Infested maize residue collected the previous season was used as the inoculum source in varying amounts; 80% coverage, 40% coverage and 0% soil coverage were used to simulate no tillage, minimum tillage and maximum tillage with complete burial of residues. In all the seasons, disease spread was adequately described by a power law model, whereas disease progress over time was equally well represented by both Gompertz and logistic models. The time factor was highly significant (P < 0.05) for disease development, indicating both increases in disease intensity over time and change in gradients with time. The amount of infested residue on the soil surface in the maize planting was highly significant (P < 0.05) for slope (b) and intercept (a) of the linearised disease gradient. The gradient parameter (b) based on the average for the four directions from the residue source ranged from ?0.96 to ?0.08 in the second cropping season of 1999, from ?2.16 to ?0.01 and from ?0.87 to ?0.03 in the first and second seasons of 2000, respectively. The distance from the infested residue significantly affected foliar disease, but the direction from the residue inoculum source did not, nor was the distance by direction interaction significant. However, interactions between amount of residue and distance were significant. Percentage leaf area affected by grey leaf spot, the areas under disease progress curves and disease intercepts decreased with distance at both locations, but rate of disease increase (r) was generally constant with distance from residue source at Kabanyolo, but not at Namulonge. The relationship between disease severity and amount of residue cover appeared to be affected by the level of background inoculum. At Kabanyolo, where little background inoculum was present, differences were detected in disease severity parameters between the no‐residue plots and residue plots, whereas at Namulonge, where high background levels existed, there was no effect of residue on disease.     

Direct plant regeneration from leaf explants of Plumbago species and its genetic fidelity through RAPD markers

In vitro plant regeneration was achieved from leaf explants of Plumbago rosea and Plumbago zeylanica on Murashige & Skoog (1962) medium supplemented with 1.5 mg litre^?1 6‐benzylaminopurine, 0.25 mg litre^?1 indole‐3‐acetic acid, 50 mg litre^?1 adenine sulfate and 3% (w/v) sucrose. The shoot initials developed within 2–3 wk on the leaf margin as well as from the wounds of the leaf. High frequency shoot‐bud regeneration was achieved on similar medium in subsequent subcultures. The semi‐mature leaves produced more shoot‐buds as compared to the younger leaves. Mature leaves did not show any response for shoot bud initiation. More than 85% of the semi‐mature explants produced shoot‐buds per leaf explant within 4 wk of culture. Shoots rooted easily on medium having half‐strength basal Murashige & Skoog (1962) medium supplemented with 0.25 mg litre^?1 indole‐3‐butyric acid and 2% (w/v) sucrose; 84–92% of the in vitro rooted plantlets survived in the greenhouse. The regenerated plantlets appeared morphologically similar to the mother plants. No variation was detected among the regenerated plants by the use of Randomly Amplified Polymorphic DNA (RAPD) markers. This method might be useful for assessing plant improvement programmes.     

Comparative studies in the morphology of Crenias weddelliana and Maferria indica with reference to Sphaerothylax abyssinica (Podostemaceae: Podostemoideae)

The scope of morphological plasticity of vegetative structures among Podostemoideae (Podostemaceae) is documented for Crenias weddelliana, a neotropical species, Maferria indica, a palaeotropical species, and Sphaerothylax abyssinica, from Kenya, and compared with related taxa. The study highlights intrinsic characters of the widely enigmatic plant body of many species of the subfamily Podostemoideae. These include dorsiventrality of shoots occurring irrespective of gravity, incurvate distichy and one‐sided spirodistichy correlated with shoot dorsiventrality, asymmetric leaves, and several types of positioning of the two prophylls and inflorescence structures. The homogeneity of hairs of the ‘Zeylanidium olivaceum type’ established on the subulate leaves of some Indian species is of taxonomic value. The latter also applies to the stipella (not stipule) on the asymmetric compound leaf in New World species. The morphological data represent a framework of features consistent for the subfamily. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 138 , 63–84.     

Uptake and transport of foliar applied zinc (65Zn) in bread and durum wheat cultivars differing in zinc efficiency

Using two bread wheat (Triticum aestivum) and two durum wheat (Triticum durum) cultivars differing in zinc (Zn) efficiency, uptake and translocation of foliar-applied ⁶⁵Zn were studied to characterize the role of Zn nutritional status of plants on the extent of phloem mobility of Zn and to determine the relationship between phloem mobility of Zn and Zn efficiency of the used wheat cultivars. Irrespective of leaf age and Zn nutritional status of plants, all cultivars showed similar Zn uptake rates with application of ⁶⁵ZnSO₄ to leaf strips in a short-term experiment. Also with supply of ⁶⁵ZnSO₄ by immersing the tip (3 cm) of the oldest leaf of intact plants, no differences in Zn uptake were observed among and within both wheat species. Further, Zn nutritional status did not affect total uptake of foliar applied Zn. However, Zn-deficient plants translocated more ⁶⁵Zn from the treated leaf to the roots and remainder parts of shoots. In Zn-deficient plants about 40% of the total absorbed ⁶⁵Zn was translocated from the treated leaf to the roots and remainder parts of shoots within 8 days while in Zn-sufficient plants the proportion of the translocated ⁶⁵Zn of the total absorbed ⁶⁵Zn was about 25%. Although differences in Zn efficiency existed between the cultivars did not affect the translocation and distribution of ⁶⁵Zn between roots and shoots. Bread wheats compared to durum wheats, tended to accumulate more ⁶⁵Zn in shoots and less ⁶⁵Zn in roots, particularly under Zn-deficient conditions. The results indicate that differences in expression of Zn efficiency between and within durum and bread wheats are not related to translocation or distribution of foliar-applied ⁶⁵Zn within plants. Differential compartementation of Zn at the cellular levels is discussed as a possible factor determining genotypic variation in Zn efficiency within wheat.     

Response of aquatic hyphomycete communities to enhanced stream retention in areas impacted by commercial forestry

1. Aquatic hyphomycetes are an important component of detritus processing in streams. Their response to enhanced stream retentiveness was tested by manipulating three streams located in Kielder Forest (northern England), a large plantation of exotic conifers, and two streams in Montagne Noire (south-west France) dominated by native broadleaf woodland. Treatment was by placement of logs or plastic litter traps into a 10–20 m stream section. Fungal spores were collected from stream water upstream and downstream of the treated sections over 1–2 years.
2. The average concentration of fungal spores in reference sections was nearly 10× greater in the French streams than in the English streams. The number of hyphomycete species was also higher in the French streams. These differences between regions were probably a consequence of the much lower standing stock and diversity of leaf litter in the English streams.
3. Despite these large regional differences, the treatment had a clear effect in all streams. Detrital standing stocks were enhanced in treated sections by up to 90% in French streams and 70% in English streams.
4. Mean spore density below treated sections increased by 1.8–14.8% in French streams and 10.2–28.9% in the naturally less retentive English streams. The number of fungal species increased significantly below the treated sections of the English streams, although not the French ones.
5. In biologically impoverished plantation streams, input of woody debris can increase detritus retention and enhance hyphomycete diversity and productivity. This may have consequent benefits for detritus processing and macroinvertebrate production.     

Growth temperature influences the underlying components of relative growth rate: an investigation using inherently fast- and slow-growing plant species

We examined the effect of growth temperature on the underlying components of growth in a range of inherently fast‐ and slow‐growing plant species. Plants were grown hydroponically at constant 18, 23 and 28 °C. Growth analysis was conducted on 16 contrasting plant species, with whole plant gas exchange being performed on six of the 16 species. Inter‐specific variations in specific leaf area (SLA) were important in determining variations in relative growth rate (RGR) amongst the species at 23 and 28 °C but were not related to variations in RGR at 18 °C. When grown at 18 °C, net assimilation rate (NAR) became more important than SLA for explaining variations in RGR. Variations in whole shoot photosynthesis and carbon concentration could not explain the importance of NAR in determining RGR at the lower temperatures. Rather, variations in the degree to which whole plant respiration per unit leaf area acclimated to the different growth temperatures were responsible. Plants grown at 28 °C used a greater proportion of their daily fixed carbon in respiration than did the 18 and 23 °C‐grown plants. It is concluded that the relative importance of the underlying components of growth are influenced by growth temperature, and the degree of acclimation of respiration is of central importance to the greater role played by NAR in determining variations in RGR at declining growth temperatures.