Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

Plant growth-promoting rhizobacteria (PGPR) are naturally occurring soil bacteria that aggressively colonize plant roots and benefit plants by providing growth promotion. Inoculation of crop plants with certain strains of PGPR at an early stage of development improves biomass production through direct effects on root and shoots growth. Inoculation of ornamentals, forest trees, vegetables, and agricultural crops with PGPR may result in multiple effects on early-season plant growth, as seen in the enhancement of seedling germination, stand health, plant vigor, plant height, shoot weight, nutrient content of shoot tissues, early bloom, chlorophyll content, and increased nodulation in legumes. PGPR are reported to influence the growth, yield, and nutrient uptake by an array of mechanisms. They help in increasing nitrogen fixation in legumes, help in promoting free-living nitrogen-fixing bacteria, increase supply of other nutrients, such as phosphorus, sulphur, iron and copper, produce plant hormones, enhance other beneficial bacteria or fungi, control fungal and bacterial diseases and help in controlling insect pests. There has been much research interest in PGPR and there is now an increasing number of PGPR being commercialized for various crops. Several reviews have discussed specific aspects of growth promotion by PGPR. In this review, we have discussed various bacteria which act as PGPR, mechanisms and the desirable properties exhibited by them.

Plant Growth Promoting Rhizobacteria: A Critical Review

Although the number of biocontrol products is increasing, these products still represent only about 1% of agricultural chemical sales. Yet these are important contributions because biocontrol agents offer disease management alternatives with different mechanisms of action than chemical pesticides. Trends in research include the increased use of biorational screening processes to identify microorganisms with potential for biocontrol, increased testing under semicommercial and commercial production conditions, increased emphasis on combining biocontrol strains with each other and with other control methods, integrating biocontrol into an overall system.

Commercialization and Implementation of Biocontrol 1

Physiological Effects of Hydrogen, Aluminum, and Manganese Toxicities in Acid Soil

Reliable, precise and accurate estimates of disease severity are important for predicting yield loss, monitoring and forecasting epidemics, for assessing crop germplasm for disease resistance, and for understanding fundamental biological processes including co-evolution. Disease assessments that are inaccurate and/or imprecise might lead to faulty conclusions being drawn from the data, which in turn can lead to incorrect actions being taken in disease management decisions. Plant disease can be quantified in several different ways. This review considers plant disease severity assessment at the scale of individual plant parts or plants, and describes our current understanding of the sources and causes of assessment error, a better understanding of which is required before improvements can be targeted. The review also considers how these can be identified using various statistical tools. Indeed, great strides have been made in the last thirty years in identifying the sources of assessment error inherent to visual rating, and this review highlights ways that assessment errors can be reduced—particularly by training raters or using assessment aids. Lesion number in relation to area infected is known to influence accuracy and precision of visual estimates—the greater the number of lesions for a given area infected results in more overestimation. Furthermore, there is a widespread tendency to overestimate disease severity at low severities (<10%). Both interrater and intrarater reliability can be variable, particularly if training or rating aids are not used. During the last eighty years acceptable accuracy and precision of visual disease assessments have often been achieved using disease scales, particularly because of the time they allegedly save, and the ease with which they can be learned, but recent work suggests there can be some disadvantages to their use. This review considers new technologies that offer opportunity to assess disease with greater objectivity (reliability, precision, and accuracy). One of these, visible light photography and digital image analysis has been increasingly used over the last thirty years, as software has become more sophisticated and user-friendly. Indeed, some studies have produced very accurate estimates of disease using image analysis. In contrast, hyperspectral imagery is relatively recent and has not been widely applied in plant pathology. Nonetheless, it offers interesting and potentially discerning opportunities to assess disease. As plant disease assessment becomes better understood, it is against the backdrop of concepts of reliability, precision and accuracy (and agreement) in plant pathology and measurement science. This review briefly describes these concepts in relation to plant disease assessment. Various advantages and disadvantages of the different approaches to disease assessment are described. For each assessment method some future research priorities are identified that would be of value in better understanding the theory of disease assessment, as it applies to improving and fully realizing the potential of image analysis and hyperspectral imagery.

Plant Disease Severity Estimated Visually, by Digital Photography and Image Analysis, and by Hyperspectral Imaging

Biological control of strawberry gray mold by Clonostachys rosea under field conditions

Suppression of Botrytis cinerea sporulation by Clonostachys rosea on rose debris: a valuable component in Botrytis blight management in commercial greenhouses

Corynespora cassiicola f. sp. lantanae: a potential biocontrol agent from Brazil for Lantana camara

Development of Clonostachys rosea in rose leaves and petals and control of Botrytis cinerea by the agent were investigated. C. rosea germinated, established endophytic growth, and sporulated abundantly whether the tissues were mature, senescent or dead when inoculated. Germination incidence was moderate on mature and senescent leaves (47% and 35%) and petals (31% and 43%), and high (>98%) on dead tissues. Sporulation of C. rosea in tissues inoculated when mature, senescent or dead averaged 41%, 61%, and 75% in leaves, and 48%, 87% and 53% in petals. When leaves were wounded with needles before inoculation, germination of C. rosea increased from 45–56% to 90–92%, but sporulation became high (> 75%) regardless of wounds. When leaves were inoculated with C. rosea at 0–24 h after wounding and subsequently with B. cinerea, germination of the pathogen was reduced by 25–41% and sporulation by ≥ 99%. A humid period prior to inoculation of senescent or dead leaves promoted communities of indigenous fungi, reduced sporulation of C. rosea and B. cinerea, and, in dead leaves, increased control of the pathogen associated with C. rosea. Applied at high density, isolates of indigenous Penicillium sp. and Alternaria alternata from rose interacted with C. rosea and reduced control of the pathogen by 16% and 21%, respectively. In conclusion, C. rosea markedly suppressed sporulation of B. cinerea in rose leaves and petals regardless of developmental stage, minor wounds, and natural densities of microflora. This versatility should allow C. rosea to effectively control inoculum production of B. cinerea in rose production systems.

Luiz A. Maffia

Papers

Biological control of strawberry gray mold by Clonostachys rosea under field conditions

Suppression of Botrytis cinerea sporulation by Clonostachys rosea on rose debris: a valuable component in Botrytis blight management in commercial greenhouses

Corynespora cassiicola f. sp. lantanae: a potential biocontrol agent from Brazil for Lantana camara

Effects of Host and Microbial Factors on Development of Clonostachys rosea and Control of Botrytis cinerea in Rose

Biological control of coffee rust by antagonistic bacteria under field conditions in Brazil