Heat stress is one of the production constraints for tomato (Solanum lycopersicum L.) due to unfavorable, above optimum temperatures. This research was undertaken to evaluate growth and fruit yield of tomato genotypes under three contrasting growing conditions (i.e., optimal temperature in field-, high temperature in field- and high temperature in greenhouse conditions) to determine their relative heat tolerance. Eleven tomato genotypes, including two local check varieties, were evaluated, and data on growth and yield were measured and analyzed. The interactions between the genotypes and growing conditions for all yield traits were significant. In general, the performance of tomato under optimal temperature field conditions was better than under high temperature field- and greenhouse conditions. Genotypes CLN1621L, CLN2026D, CLN3212C, and KK1 had consistently greater fruit yield per plant in all growing conditions. Although the local genotype, Neang Tamm, had lower yield under optimal conditions, it performed moderately well under high temperature field- and high temperature greenhouse conditions, and yield decrease under high temperature condition was minimal. Genotype CLN1621L had stable fruit setting compared to other genotypes under high temperature conditions. Since fruit setting and yield are important traits for heat tolerance, genotypes CLN1621L and Neang Tamm are potential candidates for breeding programs focused on improved yield and heat stress tolerance.

Low phosphorus (P) availability is a major limiting factor for potatoes. P fertilizer is applied to enhance P availability; however, it may become toxic when plants accumulate at high concentrations. Therefore, it is necessary to gain more knowledge of the morphological and biochemical processes associated with P deficiency and toxicity for potatoes, as well as to explore an alternative approach to ameliorate the P deficiency condition. A comprehensive study was conducted (I) to assess plant morphology, mineral allocation, and metabolites of potatoes in response to P deficiency and toxicity; and (II) to evaluate the potency of plant growth-promoting rhizobacteria (PGPR) in improving plant biomass, P uptake, and metabolites at low P levels. The results revealed a reduction in plant height and biomass 60–80% under P deficiency compared to P optimum. P deficiency and toxicity conditions also altered the mineral concentration and allocation in plants due to nutrient imbalance. The stress induced by both P deficiency and toxicity was evident from an accumulation of proline and total free amino acids in young leaves and roots. Furthermore, root metabolite profiling revealed that P deficiency reduced sugars by 50–80% and organic acids by 20–90%, but increased amino acids by 1.5–14.8 times. However, the effect of P toxicity on metabolic changes in roots was less pronounced. Under P deficiency, PGPR significantly improved the root and shoot biomass, total root length, and root surface area by 32–45%. This finding suggests the potency of PGPR inoculation to increase potato plant tolerance under P deficiency.

Increasing fruit yield and quality of tomatoes under organic low-input conditions remains a challenge for producers and breeders. Therefore, it is necessary to identify superior tomato cultivars that are suitable for production and use as parents in breeding programmes. In the present study, the variations in plant morphology and fruit quality characteristics of tomato cultivars were assessed to reveal the traits associated with improved yield and fruit quality. Sixty diverse tomato cultivars were screened in 2015, and in 2016, a subset of 20 cultivars was selected for further evaluation under organic low-input conditions. The results showed high variability among cultivars in all 28 traits that were observed. Salad cultivars had lower plant growth and fruit quality (minerals, dry matter, total soluble solids, and total phenolics) by 10–70%, but they displayed 10–60% higher fruit yield and leaf minerals than cocktail cultivars. Salad tomato cultivars with superior yield and harvest index were mainly derived from breeding for intensive indoor production. Cocktail cultivars with superior yield were mainly derived from organic and outdoor breeding programs. There was a trade-off between fruit yield and quality, indicating a challenge for simultaneous improvement of yield and quality. The importance of Mg was highlighted because of its contribution to the fruit mineral concentration and fruit quality. Cultivars superior in one trait or trait combination under organic low-input conditions were identified to be used by producers and breeders as superior cultivars to meet their production targets and breeding objectives. The importance of Mg provides a novel path for further research on improving soil-available Mg in organic tomato production to enhance fruit mineral concentration and fruit quality in general.

The limited availability of phosphorus (P) in soils causes a major constraint in the productivity of potatoes, which requires increased knowledge of plant adaptation responses in this condition. In this study, six potato cultivars, namely, Agria, Lady Claire, Milva, Lilly, Sieglinde, and Verdi, were assessed for their responses on plant growth, leaf physiology, P use efficiency (PUE), and tuber quality with three P levels (Plow, Pmed, and Phigh). The results reveal a significant variation in the cultivars in response to different P availabilities. P-efficient cultivars, Agria, Milva, and Lilly, possessed substantial plant biomass, tuber yield, and high P uptake efficiency (PUpE) under low P supply conditions. The P-inefficient cultivars, Lady Claire, Sieglinde, and Verdi, could not produce tubers under P deprivation conditions, as well as the ability to efficiently uptake P under low-level conditions, but they were efficient in P uptake under high soil P conditions. Improved PUpE is important for plant tolerance with limited P availability, which results in the efficient use of the applied P. At the leaf level, increased accumulations of nitrate, sulfate, sucrose, and proline are necessary for a plant to acclimate to P deficiency-induced stress and to mobilize leaf inorganic phosphate to increase internal PUE and photosynthesis. The reduction in plant biomass and tuber yield under P-deficient conditions could be caused by reduced CO2 assimilation. Furthermore, P deficiency significantly reduced tuber yield, dry matter, and starch concentration in Agria, Milva, and Lilly. However, contents of tuber protein, sugars, and minerals, as well as antioxidant capacity, were enhanced under these conditions in these cultivars. These results highlight the important traits contributing to potato plant tolerance under P-deficient conditions and indicate an opportunity to improve the P efficiency and tuber quality of potatoes under deficient conditions using more efficient cultivars. Future research to evaluate molecular mechanisms related to P and sucrose translocation, and minimize tuber yield reduction under limited P availability conditions is necessary.

Legume production under infertile sandy soil may be limited by low nitrogen (N) and phosphorus (P) availability in the soil. A study was conducted to assess the effects of N and P on growth, yield, and root nodules of mung bean under sandy soil conditions. Two pot experiments were conducted under a greenhouse environment and were laid out in a completely randomized design (CRD) with five replications. Experiment 1 consisted of two types of soils (sandy and loamy sand) and two P application rates at 0 and 13 mg P kg-1. Experiment 2 consisted of 10 fertilizer treatments that included two N treatments of 0 and 53 mg N kg-1 in combination with four P treatments of 0, 17, 34, 68 mg P kg-1, P only at 17 mg P kg-1, and a cattle manure that was applied at a rate of 5 t ha-1 which was equivalent to 52:07:56 (N:P:K mg kg-1). The results showed that crop growth and root nodules improved with P application in the loamy sand soil (containing medium P), but not in the sandy soil (containing low P). Nitrogen application also improved the crop growth and grain yield significantly in loamy sand soil. However, N application suppressed root nodule formation, an effect that was significant for the N2 fixation of the crop. Increase in the P rate did not alleviate the inhibitory effect of N on nodule formation. Since N and P fertilizer had opposite effects on root nodules, interactions between N and P need to be further investigated when considering the economic benefits of using these fertilizers.