The effect of six phosphate-solubilizing fungi (PSF, two strains of Aspergillus awamori , and four of Penicillium citrinum ) isolated from rhizosphere of various crops, was observed on the growth and seed production of chickpea plants ( Cicer arietinum L. cv. GPF2) in pot experiments. The phosphate (P) solubilizing activity of PSF in liquid varied from 38 to 760 μg ml −1 for tricalcium phosphate (TCP) and 28–248 μg ml −1 for mussoorie rock phosphate (MRP). All PSF isolates were biocompatible and produced growth-promoting hormone, Indole acetic acid (IAA), varying in concentration from 2.5 to 9.8 μg ml −1 . Of the various pot experiments carried out in green house, maximum stimulatory effect on chickpea plants growth was observed by inoculation of two A. awamori strains. This treatment resulted in 7–12% increase in shoot height, nearly three-fold increase in seed number and two-fold increase in seeds weight as compared to the control (un-inoculated) plants. Inoculation of four strains of P. citrinum exhibited lesser stimulatory effect. It showed 7% increase in shoot height, two-fold increase in seed number and 87% increase in seeds weight as compared to the control plants. However, a consortium of all the six fungal isolates showed no stimulatory effect on chickpea plants growth.

Stimulatory effect of phosphate-solubilizing fungal strains (Aspergillus awamori and Penicillium citrinum) on the yield of chickpea (Cicer arietinum L. cv. GPF2)

Isolation and identification of phosphate solubilizing bacteria able to enhance the growth and aloin-A biosynthesis of Aloe barbadensis Miller.

The effectiveness of autochthonous plant growth-promoting rhizobacteria was studied in Lavandula dentata and Salvia officinalis growing in a natural arid Mediterranean soil under drought conditions. These bacteria identified as Bacillus megaterium (Bm), Enterobacter sp. (E), Bacillus thuringiensis (Bt), and Bacillus sp. (Bsp). Each bacteria has different potential to meliorate water limitation and alleviating drought stress in these two plant species. B. thuringiensis promoted growth and drought avoidance in Lavandula by increasing K content, by depressing stomatal conductance, and it controlled shoot proline accumulation. This bacterial effect on increasing drought tolerance was related to the decrease of glutathione reductase (GR) and ascorbate peroxidase (APX) that resulted sensitive indexes of lower cellular oxidative damage involved in the adaptative drought response in B. thuringiensis-inoculated Lavandula plants. In contrast, in Salvia, having intrinsic lower shoot/root ratio, higher stomatal conductance and lower APX and GR activities than Lavandula, the bacterial effects on nutritional, physiological and antioxidant enzymatic systems were lower. The benefit of bacteria depended on intrinsic stress tolerance of plant involved. Lavadula demonstrated a greater benefit than Salvia to control drought stress when inoculated with B. thuringiensis. The bacterial drought tolerance assessed as survival, proline, and indolacetic acid production showed the potential of this bacteria to help plants to grow under drought conditions. B. thuringiensis may be used for Lavandula plant establishment in arid environments. Particular characteristic of the plant species as low shoot/root ratio and high stomatal conductance are important factors controlling the bacterial effectiveness improving nutritional, physiological, and metabolic plant activities.

Differential activity of autochthonous bacteria in controlling drought stress in native Lavandula and Salvia plants species under drought conditions in natural arid soil.

Native plant growth promoting bacteria Bacillus thuringiensis and mixed or individual mycorrhizal species improved drought tolerance and oxidative metabolism in Lavandula dentata plants.

Plant preparations that convert tryptophan to indoleacetic acid (IAA) characteristically have low reaction yields. Since such preparations sometimes also contain IAA-oxidase activity, inhibition of the oxidase might raise the yields of IAA. Accordingly, polyphenolic inhibitors (1, 11, 19, 33, 40) were added to incubation mixtures containing tryptophan and a seedling enzyme preparation that was able to convert tryptophan to IAA. More than tenfold increases in auxin yield resulted. However, the presence of auxin in enzymeless controls, plus experiments on the recovery of added IAA, indicated that the enhancements observed might be caused by a polyphenolic oxidation of tryptophan to IAA. We shall present evidence that the sequence

L. G. Paleg

Papers

Observations on the Quantitative Determination of Indoleacetic Acid