Show that tomato leaf phyllosphere bacteria are candidates for biocontrol of tomato leaf diseases. Seven bacterial isolates from surface sterilized, Moneymaker tomato plants were tested for growth inhibition of 14 tomato pathogens on PDA. Biocontrol assays were conducted with tomato leaf pathogens, Pseudomonas syringae pv. tomato (Pto) and Alternaria solani (A. solani). Two potential isolates showing the greatest inhibition were identified by 16s rDNA sequencing as Rhizobium sp. (isolate b1) and Bacillus subtilis (isolate b2), both produce protease and isolate b2 cellulase. Both reduced tomato leaf infections by Pto and A. solani in detached leaf bioassays. Both bacteria b1 and b2 reduced pathogen development in a tomato growth trial. Bacteria b2 also induced the tomato plant salicylic acid (SA) immune response pathway. Disease suppression in biocontrol assays with b1 and b2 varied between 5 commercial tomato varieties. Tomato phyllosphere bacteria when used as phyllosphere inoculants, inhibited tomato diseases caused by Pto and A. solani.

The use of plant growth-promoting rhizobacteria presents a promising addition to conventional mineral fertilizer use and an alternative strategy for sustainable agricultural crop production. However, genotypic variations in the plant host may result in variability of the beneficial effects from these plant–microbe interactions. This study examined growth promotion effects of commercial vegetable crop cultivars of tomato, cucumber and broccoli following application with five rhizosphere bacteria. Biochemical assays revealed that the bacterial strains used possess several nutrient acquisition traits that benefit plants, including nitrogen fixation, phosphate solubilization, biofilm formation, and indole-3-acetic acid (IAA) production. However, different host cultivars displayed genotype-specific responses from the inoculations, resulting in significant (p < 0.05) plant growth promotion in some cultivars but insignificant (p > 0.05) or no growth promotion in others. Gene expression profiling in tomato cultivars revealed that these cultivar-specific phenotypes are reflected in differential expressions of defense and nutrient acquisition genes, suggesting that plants can be categorized into “microbe-friendly” cultivars (with little or no defense responses against beneficial microbes) and “microbe-hostile” cultivars (with strong defense responses). These results validate the notion that “microbe-friendly” (positive interaction with rhizosphere microbes) should be considered an important trait in breeding programs when developing new cultivars which could result in improved crop yields.

Rhizosphere bacteria can provide multiple benefits to plants, including increased nutrient supply, pathogen/disease control, and abiotic stress tolerance, but results from pot trials do not always translate to field conditions. This study tested whether rhizosphere biocontrol bacteria can also provide plant growth promotion and how benefits can be provided at a commercial farm. Commercial lettuce seeds and plants were treated with rhizosphere biocontrol bacteria Bacillus velezensis UQ9000N, B. amyloliquefaciens 33YE, Brevibacillus laterosporus 4YE, and Pseudomonas azotoformans UQ4510An. 33YE increased the head diameter, plant height, and fresh weight of the Green Moon cultivar, while 33YE, UQ4510An, and UQ9000N increased the fresh and dry weight of Liston, a more heat-tolerant cultivar, via a single seed treatment or repeat root treatments under nursery and field conditions across different inoculation schedules and growth stages. Significant growth promotion was also demonstrated when inoculating field plants after transplanting (in particular for 33YE). Applications of these microbial biostimulants to lettuce seeds or plantlets potentially enable earlier transplanting and earlier harvests. Repeat inoculations using irrigation water and long-lasting formulations may further advance the benefits of these biostimulants as microbial biofertilisers for plant growth promotions in the field.

Crop losses can occur at various stages of production and the supply chain. However, estimating losses only at the processing stage limits our understanding of crop losses. In the macadamia production system, the extent of losses at the pre-harvest, shed, and factory reject stages has not been established. This study investigated the causes, relative magnitude, and impact of losses across the three key production stages. Crop loss data were collected fortnightly from fruit-set to harvest, and kernel quality data were obtained from factory assessments. Data from nine commercial macadamia farms in three Australian-growing regions across two seasons were analysed, which showed that the magnitude of loss varied by production stage and season. Shed rejects accounted for the highest losses of 10% of potential yield after fruit set. A marginal positive correlation (R2 = 0.39, ρ= 0.055) was observed between shed and factory rejects, but no correlation existed between pre-harvest and shed or factory rejects. Insect damage was one of the dominant contributors to crop loss across all production stages, accounting for 33% - 40% of pre-harvest losses, 13% - 16% of shed losses, and approximately 39% of factory rejects. However, insect-related losses showed no significant relationships (ρ = 0.25-0.35) across production stages, indicating that the example main damage factor was not consistently found at the postharvest stages. These findings highlight the importance of multi-stage crop-loss assessment in macadamia systems, as loss magnitude and dominant damage factors differed across production stages and were not consistently linked between stages.