Multiple species of Colletotrichum can cause bitter rot disease of apple, but the identities and relative representation of the species causing the disease in Kentucky are unknown. In total, 475 Colletotrichum isolates were collected from diseased apple fruit in 25 counties and characterized both morphologically and by using various molecular approaches. Multigene sequence analyses revealed that sample isolates belonged to several newly erected species within the Colletotrichum acutatum and C. gloeosporioides species complexes. The isolates were identified as C. fioriniae and C. nymphaeae, which reside within the C. acutatum species complex, and C. siamense, C. theobromicola, and C. fructicola, which are placed within the C. gloeosporioides species complex. C. fioriniae was the most common species causing bitter rot in Kentucky, comprising more than 70% of the isolates. Infectivity tests on detached fruit showed that C. gloeosporioides species-complex isolates were more aggressive than isolates in the C. acutatum species complex. However, isolates within the C. acutatum species complex produced more spores on lesions compared with isolates within the C. gloeosporioides species complex. Aggressiveness varied among individual species within a species complex. C. siamense was the most aggressive species identified in this study. Within the C. acutatum species complex, C. fioriniae was more aggressive than C. nymphaeae, causing larger, deeper lesions. Apple cultivar did not have a significant effect on lesion development. However, Colletotrichum spp. produced more spores on ‘Red Stayman Winesap’ than on ‘Golden Delicious’. Fungicide sensitivity tests revealed that the C. acutatum species complex was more tolerant to thiophanate-methyl, myclobutanil, trifloxystrobin, and captan compared with the C. gloeosporioides species complex. The study also revealed that mycelial growth of C. siamense was more sensitive to tested fungicides compared with C. fructicola and C. theobromicola. These research findings emphasize the importance of accurate identification of Colletotrichum spp. within each species complex, because they exhibit differences in pathogenicity and fungicide sensitivity.
Water scarcity is a major constraint in arid and semi-arid regions. Crops that require less irrigation water and those, which are considered drought-tolerant such as date palm (Phoenix dactylifera L.), are dominant in these regions. Despite the tolerance of these crops, the development of technologies that ensure efficient use of irrigation water is imperative. Taking these issues into consideration, the study was conducted to investigate the impact of limited irrigation water using a new subsurface irrigation system (SSI) on gas exchange, chlorophyll content, water use efficiency, water productivity, fruit physicochemical characteristics, and yield of date palm (cv. Sheshi). The impact of the SSI system was compared with two surface irrigation systems, namely, surface drip irrigation (SDI) and surface bubbler irrigation (SBI). The field experiment was carried out during 2018 and 2019 at the Date Palm Research Center of Excellence, King Faisal University, Kingdom of Saudi Arabia. The annual crop evapotranspiration (ETc) was 2544 mm. The applied irrigation water was set at 50%, 75%, and 125% of ETc for SSI, SDI, and SBI, respectively, which were based on the higher crop water productivity recorded in an initial field study. The total annual volume of water applied for SSI, SDI, and SBI was 22.89, 34.34, and 57.24 m3 palm−1, respectively. The crop water productivity (CWP) at the SSI system was significantly higher, with a value of 1.15 kg m−3, compared to the SDI (0.51 kg m−3) and SBI systems (0.37 kg m−3). The photosynthetic water use efficiency (WUE) was 10.09, 9.96, and 9.56 μmol CO2 mmol−1 H2O for SSI, SBI, and SDI, respectively. The maximum chlorophyll content (62.4 SPAD) was observed in SBI, followed by SSI (58.9 SPAD) and SDI (56.9 SPAD). Similarly, net photosynthesis and the transpiration rate were significantly higher in SBI and lowest in SSI. However, the SSI system substantially increased palm yield and enhanced fruit quality. The new SSI system, through its positive impact on the efficiency of irrigation water use and enhancement on fruit yield and fruit quality of date palm, seems quite suitable for the irrigation of palm trees in arid and semi-arid regions.
A model has been developed that can be used to determine the phases of sensitivity to photoperiod for seedlings subjected to reciprocal transfers at regular intervals between long (LD) and short day (SD) conditions. The novel feature of this approach is that it enables the simultaneous analysis of the time to flower and number of leaves below the inflorescence. A range of antirrhinum cultivars were grown, all of which were shown to be quantitative long-day plants. Seedlings were effectively insensitive to photoperiod when very young (juvenile). However, after the end of the juvenile phase, SD delayed flowering and increased the number of leaves below the inflorescence. Plants transferred from LD to SD showed a sudden hastening of flowering and a decrease in leaf number once sufficient LD had been received for flower commitment. Photoperiod had little effect on the rate of flower development. The analysis clearly identified major cultivar differences in the length of the juvenile phase and the photoperiod-sensitive inductive phase in both LD and SD.
Abstract:The entomopathogenic bacterium, Xenorhabdus nematophila was isolated from the hemolymph of Galleria mellonella infected with Steinernema carpocapsae. The bacterial cells and its metabolic secretions have been found lethal to the Galleria larvae. Toxic secretion in broth caused 95% mortality within 4 d of application whereas the bacterial cells caused 93% mortality after 6 d. When filter and sand substrates were compared, the later one was observed as appropriate. Similarly, bacterial cells and secretion in broth were more effective at 14% moisture and 25 °C temperature treatments. Maximum insect mortality (100%) was observed when bacterial concentration of 4×10 6 cells/ml was used. Similarly, maximum bacterial cells in broth (95%) were penetrated into the insect body within 2 h of their application. However, when stored bacterial toxic secretion was applied to the insects its efficacy declined. On the other hand, when the same toxic secretion was dried and then dissolved either in broth or water was proved to be effective. The present study showed that the bacterium, X. nematophila or its toxic secretion can be used as an important component of integrated pest management against Galleria.
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