Stomatal conductance (gs) and transpiration rates vary widely across plant species. Leaf hydraulic conductance (k leaf) tends to change with g (s), to maintain hydraulic homeostasis and prevent wide and potentially harmful fluctuations in transpiration-induced water potential gradients across the leaf (Delta Psi leaf). Because arbuscular mycorrhizal (AM) symbiosis often increases gs in the plant host, we tested whether the symbiosis affects leaf hydraulic homeostasis. Specifically, we tested whether k leaf changes with gs to maintain Delta Psi leaf or whether Delta Psi leaf differs when gs differs in AM and non-AM plants. Colonization of squash plants with Glomus intraradices resulted in increased gs relative to non-AM controls, by an average of 27% under amply watered, unstressed conditions. Stomatal conductance was similar in AM and non-AM plants with exposure to NaCl stress. Across all AM and NaCl treatments, k leaf did change in synchrony with gs (positive correlation of gs and k leaf), corroborating leaf tendency toward hydraulic homeostasis under varying rates of transpirational water loss. However, k leaf did not increase in AM plants to compensate for the higher gs of unstressed AM plants relative to non-AM plants. Consequently, Delta Psi leaf did tend to be higher in AM leaves. A trend toward slightly higher Delta Psi leaf has been observed recently in more highly evolved plant taxa having higher productivity. Higher Delta Psi leaf in leaves of mycorrhizal plants would therefore be consistent with the higher rates of gas exchange that often accompany mycorrhizal symbiosis and that are presumed to be necessary to supply the carbon needs of the fungal symbiont.

Arbuscular mycorrhizal (AM) fungi are commonly occurring soil microbes whose association with roots can have wide ranging effects on growth of the host plants. These fungi are frequent root colonizers of trees, shrubs, terrestrial orchids and a broad range of plants in temperate and tropical habitats. During the establishment of AM symbiosis, a range of chemical and biological parameters are affected in plants. These fungi are considered instrumental in promoting plant establishment and growth in these environments by enhancing plant nutrient and water uptake, protecting plants from root herbivores and pathogens and improving soil structure. This symbiosis is alleged to improve plant resistance to drought and nutrient stress. There are several reports which show that AM induce physiological drought tolerance, involving both increased dehydration avoidance and dehydration tolerance. Majority of the experiments have shown that when the symbiosis improves host drought resistance it does so by aiding drought avoidance. AM symbiosis has frequently increased resilience of host plants to salinity stress. The AM plants in the saline soils had increased phosphate and decreased Na concentrations in shoots compared to non-AM ones. Salt resistance has been shown to improve by AM colonization in a number of crops like maize, mungbean, clover, cucumber, lettuce, tomato, and many more. A correlation has been established between AM colonization and improved osmoregulation or proline accumulation. AM colonization has also been documented to improve NaCl resistance in tomato, with the extent of improvement related to salt sensitivity of a cultivar. AM improvement of salt resistance has usually been associated with AM-induced increases in P acquisition and plant growth. However, there are scanty reports of AM induced effects on host plants being more pronounced when plants were exposed to osmotic stress in salinized soils.

In this study Penicillium implicatum was found to be the cause of postharvest rot of stored pomegranate (Punica granatum L.) fruit. Rot symptom was observed on pomegranate fruit as small, sunken, circular to oval, dark brown necrotic spots. Infected fruit tissues were cultured on malt extract agar (MEA), Czapek (Cz), Czapek yeast Agar (CYA) and G25N media at 25°C. This fungal species was primarily characterized by its relatively slow growth on MEA, Cz, CYA and G25N, blue-grey sporulation, forming crusts, production of a soluble yellow pigment on the media and inability to grow at 5 and 37°C on both Cz and MEA. Microscopically, it was characterized by its long, smooth-walled and vesiculate conidiophores and smooth ellipsoidal to ovoid, up to 3.5 μm long, conidia. The fungus was identified as P. implicatum on the basis of morphological and cultural characteristics. Pathogenicity tests conducted on healthy fruits under laboratory conditions showed typical rot symptoms after 7 to 14 days. This is the first report of postharvest rot of pomegranate caused by P. implicatum in Pakistan.Keywords Punica granatum . Penicillium implicatum . Fruit rot . PomegranatePenicillium is one of the major causes of spoilage of agricultural products during pre and post harvest phase. In December 2010, during a survey of local fruit market in Lahore (Pakistan), irregular brown to caramel-brown spots were observed on the skin of pomegranate fruits (Punica granatum L.). To clarify the causal agents of those symptoms, fruit samples were obtained from a local fruit market, kotlakhpat, Lahore and examined at laboratory. From the necrotic areas, a blue-grey fungal growth was observed. Temporary slides of diseased tissues were made and observed under light microscope. Small pieces (3 mm) of rotting tissue from the fruits and surface sterilized with 1 % Na(O)Cl, were placed onto 2 % malt extract agar (MEA) and incubated at 25°C in darkness for 5 days. As a result, a species belonging to the genus Penicillium subgenus Aspergilloides was consistently found associated to the described symptoms. A recent record proves that P. implicatum Biourge (subgenus Aspergilloides) was the causal agent of a similar fruit rot in Slovak Republic (Labuda et al. 2004). According to key (Raper and Thom 1949;Pitt 1979Pitt , 1985 Ramírez 1982;Samson et al. 1995; Pitt and Hocking 1997) this species is primarily characterized by its relatively slow growth on Czapek-based media and MEA at 25°C, heavy blue-grey sporulation, forming crusts, production of a soluble yellow pigment on the media, and inability to grow at 5 and 37°C on both Cz and MEA. Thus, in order to allow the confirmation of the fungus identity obtained in this study the resulting fungal colonies were subcultured on Czapek-solution agar (Cz), 2 % MEA, CYA and G25N at 25°C for 7 to 14 days according to Pitt (1979). The description of our fungal specimen is as follow: On Cz medium, colonies 20-25 mm diam., surface velutinous, somewhat floccose in the centres, plane, centrally raised or crateriform...

No abstract

No abstract