Experimental assessment of the contribution of plant root respiration to the emission of carbon dioxide from the soil

The contributions of root and microbial respiration to the total emission of CO₂ from the surface of gray forest and soddy-podzolic soils were compared under laboratory and field conditions for the purpose of optimizing the field version of the substrate-induced respiration method. The magnification coefficients of respiration upon the addition of saccharose (k _mic) were first determined under conditions maximally similar to the natural conditions. For this purpose, soil cleared from roots was put into nylon nets with a mesh size of 40 μm to prevent the penetration of roots into the nets. The nets with soil were left in the field for 7–10 days for the compaction of soil and the stabilization of microbial activity under natural conditions. Then, the values of k _mic were determined in the root-free soil under field conditions or in the laboratory at the same temperature and water content. The contribution of root respiration as determined by the laboratory version of the substrate-induced respiration method (7–36%) was lower compared to two field versions of the method (27–60%). Root respiration varied in the range of 24–60% of the total CO₂ emission from the soil surface in meadow ecosystems and in the range of 7–56% in forest ecosystems depending on the method and soil type.     

Biochemical changes in duck weed after cadmium treatment. Enhancement in senescence

The effect of Cd on biochemical changes in the free floating duck weed (Spirodela polyrrhiza L. SP₂₀) was studied. Cadmium enhanced senescence; enzymes like peroxidase, protease and phosphatases, which are known as a marker of senescence, were increased after Cd treatment. Nitrate reductase activity was also increased. With increasing Cd levels, Ca, Mg, and Zn concentrations in the plant were decreased while the Fe concentration was increased.     

Biofortification of taro (Colocasia esculenta) through breeding for increased contents in carotenoids and anthocyanins

Biofortification of taro (Colocasia esculenta) has never been studied. The aim of the present study is to compare the chemical compositions and individual constituent contents for major compounds (starch, sugars, cellulose, proteins, minerals), carotenoids and anthocyanins between parents and hybrids selected first for their agronomic performance and second for their corm characteristics (flesh color, quality and taste). For major compounds, 45 selected hybrids were compared to 66 cultivars and for carotenoids and anthocyanins, 34 selected hybrids were compared to 79 cultivars. Total sugars, cellulose and mineral contents presented moderate increases in hybrids. Carotenoids and anthocyanins contents were not correlated with corm flesh colors, most likely in relation with the wide range of the observed variability. Anthocyanin contents could not be increased in the selected hybrids, while total carotenoid contents were increased by more than fourfolds. The results of this study indicate that carotenoid contents can be rapidly improved by selecting plants of good agronomic performance and corm shape with increased density of yellow and orange colors. Potential applications to taro breeding programs are discussed.     

Biological study of Plutella xylostella (L.) (Lep: Plutellidae) and it's solitary endoparasitoid, Cotesia vestalis (Haliday) (Hym. Braconidae) under laboratory conditions

Plutella xylostella (L.) (Lep: Plutellidae), is a destructive pest of brassicaceous crops in the world. Cotesia vestalis (Haliday) is one of most important biological control agents of P. xylostella in the world and Iran. Both of P. xylostella and C. vestalis biology were carried out in laboratory condition. Results showed that development time of immature stages of P. xylostella including egg, Instar I, Instar II, Instar III, Instar IV, prepupa, pupa were 2.39 +/- 0.17, 2.18 +/- 0.17, 2.06 +/- 0.28, 2.14 +/- 0.14, 2.54 +/- 0.12, 0.40 +/- 0.12 and 4.23 +/- 0.23 days, respectively. Longevity of female and male were 28.26 +/- 0.05 and 30.22 +/- 0.05 days. By dissecting the parasitized larvae, the egg incubation period of C. vestalis was recorded 1.73 +/- 0.06 days. In long-term oviposition trials, females laid eggs on P. xylostella larvae for up to 10 days. Larval development of the parasitoid in host only required 6.47 days: the first instar larva required 3.25 +/- 0.047 days; the second instar larva needed 2.78 +/- 0.1 days and the third instar larvae exited the host and pupated in, 0.4 +/- 0.07 days. Prepupal and pupal period of wasp were 1.9 +/- 0.06 and 2.13 +/- 0.09 day, respectively. Unmated female and male longevity of wasp were 16.83 +/- 0.37, 16.25 +/- 0.17 and sex ratio is male-biased. When a mixed group and isolated of instars were presented for parasitoid, the 2nd and 3rd instar larvae were so preferred and the 4th instar was less attractive for selection. In choice experiment, the percentage parasitism of 2nd, 3rd and 4th instars was 78.58, 69.94 and 4.36%, respectively. The rapid oviposition rate, short life duration and high percentage parasitism increases parasitoid potential for suppression of host population. Present results suggest that C. vestalis has considerable potential as a biological control agent for P. xylostella.     

Morphological, anatomical and molecular investigation into witches’ broom disease of mamejvo (Enicostemma axillare)

Mamejvo (Enicostemma axillare Raynal) is a perennial herb with diversified health benefits. It was found to be affected by a witches?? broom disease under the field conditions at Anand, Gujarat, India. Affected plants were 53.33% reduced in height due to shortened internodes, leading to typical witches?? broom symptoms. Flower size was reduced significantly in the affected plants compared with the healthy ones and their petal color gradually turned green (virescence). Affected plants produced 2.5 times more dry herbage than the normal plants but with less active ingredient (swertiamarin). Symptomatic plants died early while root suckers from such plants failed to establish after transplanting. DAPI stained transverse sections of affected shoot tips showed the presence of discrete greenish fluorescence in the phloem cells under UV light. Amplification of 1.2?kb phytoplasma specific rDNA fragment from diseased tissue confirmed the presence of the pathogen. Further characterization of the pathogen through virtual rDNA?CRFLP pattern and rDNA sequence based phylogeny suggested that the pathogen, Enicostemma witches?? broom phytoplasma, belonged to 16SrII?CC group of ??Ca Phytoplasma aurantifolia??.     

SoilFlex‐LLWR: linking a soil compaction model with the least limiting water range concept

Soil compaction impacts growing conditions for plants: it increases the mechanical resistance to root growth and modifies the soil pore system and consequently the supply of water and oxygen to the roots. The least limiting water range (LLWR) defines a range of soil water contents within which root growth is minimally limited with regard to water supply, aeration and penetration resistance. The LLWR is a function of soil bulk density (BD), and hence directly affected by soil compaction. In this paper, we present a new model, ‘SoilFlex‐LLWR’, which combines a soil compaction model with the LLWR concept. We simulated the changes in LLWR due to wheeling with a self‐propelled forage harvester on a Swiss clay loam soil (Gleyic Cambisol) using the new SoilFlex‐LLWR model, and compared measurements of the LLWR components as a function of BD with model estimations. SoilFlex‐LLWR allows for predictions of changes in LLWR due to compaction caused by agricultural field traffic and therefore provides a quantitative link between impact of soil loading and soil physical conditions for root growth.