The Australian sugar industry has never pursued genetic resistance to ratoon stunting disease (RSD), despite it being widely considered to be one of the most important diseases of sugarcane (Saccharum interspecific hybrids). This is because of a prevailing view that the disease is economically managed, and that no further action needs to take place. However, there is a range of epidemiological evidence that suggests that RSD is having a more significant impact than what is generally recognized. This review traces the factors that have led to an industry stance that is apparently without any scientific justification, and which has tended to downplay the significance of RSD on Australian sugarcane productivity, and thus has led to significant lost production. The consequences of this position are that RSD may be influencing broad but poorly explained issues such as commercial ratooning performance of existing varieties and the “yield decline” that has been subject to much scrutiny, if not much success in resolving the issue. Based on the available information, this review calls on the Australian sugar industry to prioritize selection for RSD resistance in the plant improvement program.
Chilli pepper (Capsicum spp.) is an important crop with increasing global consumption; the top three chilli pepper-producing countries are China, Mexico and Indonesia (FAOSTAT, 2023). One of the main bacterial diseases of chilli pepper is bacterial leaf spot which causes yield loss due to damaged and unsaleable fruits (Utami et al., 2022). The disease has been reported in Indonesia but there is no information about the causal agent. In April and May 2022, bacterial leaf spots were observed in a commercial plantation in Bantul, Yogyakarta, Indonesia (8°00'5.5" S and 110°18'46.9" E). Small black lesions were observed on the leaves (Figure 1a). These lesions were surrounded by yellow circles or irregular, dark brown or black greasy spots (Figure 1b). A total of 100 diseased leaves were collected and surface-sterilised with 70% ethanol then wiped with absorbent paper. Squares containing individual lesions were excised from the samples using a sterile scalpel and bisected. One half of each lesion was placed on a drop of sterile water on a microscope slide and overlaid with a coverslip to inspect for oozing (×100 magnification), the other half was placed in an another drop of water for culturing and as a crude PCR template. Bacterial oozing was observed in almost all lesions sectioned. For six ooze-positive samples, bacteriological streaks on nutrient agar plates supplemented with 2% starch were made from the second set of samples. Plates were sealed with plastic film and incubated for 48 hours at 28°C. Following isolation and successive subculturing (×3) from single colonies, one isolate was obtained (BY1) and an amylase test (Schaad et al., 2001) was conducted to differentiate X. euvesicatoria pv. euvesicatoria from X. vesicatoria and X. euvesicatoria pv. perforans which also cause bacterial leaf spot. After incubation at 28°C for 48 hours, three drops of 10% iodine solution were added onto the edge of the colonies and were observed as amylase-negative owing to the lack of clearing in the medium. The bacterium was further identified by molecular characterisation. Six primer pairs Xeu2.4/Xeu2.5 (Moretti et al., 2009), gyrB-F/gyrB-R (Kyeon et al., 2016), and Bs-XeF/Bs-XeR, Bs-XvF/Bs-XvR, Bs-XgF/Bs-XgR and Bs-XpF/Bs-XpR (Koenraadt et al., 2009) were used to screen ooze samples as well as aqueous suspensions of pure cultures of the isolated bacterium. Aqueous suspensions were made by picking a single colony with a sterile pipette tip and swirling in 100 μl distilled water. PCR was performed using 12.5 μl 2X Phire reaction buffer (Thermo Fisher Scientific, USA), 0.5 μl of each primer (10 μM), 10.5 μl Milli-Q water, and 1 μl template with the following thermocycle: 95°C for 5 minutes followed by 40 cycles of 95°C for 20 secs, 64°C for 30 secs, and 72°C for 25 secs, followed by 72°C for seven minutes. The PCR products amplified with gyrB-F/gyrB-R and Xeu2.4/Xeu2.5 were sequenced and the sequences deposited in GenBank (Accession Nos. OQ943232 and OQ943233). Trimmed sequences were aligned with reference sequences of Xanthomonas spp. and the gyrB gene region showed 99.85% identity to X. euvesicatoria pv. euvesicatoria (KY658944.1 and EU015388.1) (Figure 2). The region amplified using the Xeu2.4/Xeu2.5 primers was identical to X. campestris pv. vesicatoria AM039952.1, a strain now classified as X. euvesicatoria pv. euvesicatoria (Figure 3). A pathogenicity trial was conducted in a greenhouse using two chilli pepper species (C. frutescens cv. Trisula Hijau and C. annuum var. annuum). The isolate was grown on nutrient agar and incubated for 48 hours at 28°C. Single colonies obtained from the pure cultures were suspended in distilled water and adjusted to 1 × 108 CFU/ml. Three five-week-old chilli pepper plants were inoculated with the bacterial suspension by spraying 1 ml bacterial suspension per leaf. Control plants were treated with sterile distilled water. Black spot symptoms, consistent with those observed in the field, were seen after four days in both chilli pepper species but no symptoms were seen on control plants. Symptoms on inoculated plants were ooze-positive, and the ooze was confirmed positive for X. euvesicatoria pv. euvesicatoria using the Xeu2.4/Xeu2.5 and gyrB-F/gyrB-R primers. Based on the biochemical, molecular and pathogenicity tests, the strain isolated from chilli pepper in Indonesia was identified as X. euvesicatoria pv. euvesicatoria. Bacterial leaf spot on chilli pepper has probably existed for some time in Indonesia but this is the first report of the aetiology of the disease. This research was supported by Australia Awards Scholarship- John Allwright Fellowship 2019–2023 and ACIAR SLAM/2018/145.
Characteristic leaf spot and blight symptoms caused by Robbsia andropogonis on bougainvillea plants were found in three locations in different provinces of Mexico from 2019 to 2020. Eleven bacterial isolates with morphology similar to R. andropogonis were obtained from the diseased bougainvillea leaves. The isolates were confirmed as R. andropogonis by phenotypic tests and 16S rRNA, rpoD, and gyrB gene sequencing. In addition to bougainvillea, the strains were pathogenic to 10 agriculturally significant crops, including maize (Zea mays), sorghum (Sorghum bicolor), barley (Hordeum vulgare), coffee (Coffea arabiga), carnation (Dianthus caryophilus), Mexican lime (Citrus × aurantifolia), common bean (Phaseolus vulgaris), broadbeans (Vicia faba), and pea (Pisum sativum), but not runner bean (Phaseolus coccineus). The haplotypes network reveals the genetic variability among Mexican strains and its phylogeographic relationship with Japan, the U.S.A., and China. The presence of this pathogen represents a challenge for plant protection strategies in Mexico.
Abstract Fertilisers are essential in modern agriculture to enhance plant growth, crop production and product quality. Recent research has focused on the development of delivery systems designed to prolong fertiliser release. This study introduces a new technology to encapsulate and release molecules of fertilisers by using multi-layered electrospun nanofibre as a carrier. Single-layer poly L-lactic acid (PLLA) nanofibres loaded with urea were fabricated using electrospinning. Triple-layer nanofibrous structures were produced by electrospinning polyhydroxybutyrate (PHB) nanofibres as external layers with PLLA nanofibres impregnated with urea fertiliser as the middle layer. Scanning electron microscopy (SEM) and Fourier transform infrared spectrophotometry (FTIR) were employed to characterize the morphology of electrospun nanofibres. Urea release dynamic was analysed using a total nitrogen instrument (TNM-1). The results indicated that triple-layered urea-impregnated nanofibrous structures led to lower initial rate of nitrogen release and slower release rate of cumulative nitrogen which extended for more than three months. It is concluded that triple-layer nanofibrous structures have the potential for slow release delivery of fertilisers.
Ziziphus mauritiana Lam. (Rhamnaceae) (Chinee Apple, Indian Jujube, or Ber) is a significant woody weed in the drier tropics of northern Queensland, Western Australia, and the Northern Territory. Throughout these regions, its densely formed thickets influence the structure, function, and composition of rangeland ecosystems by outcompeting native pasture species. Despite this, the recent literature is heavily focused on the horticultural value of domesticated Ziziphus species in South Asia (China, India, and Pakistan), particularly its potential for poverty alleviation in arid or semi-arid areas. In fact, there has been comparatively little research undertaken on its invasiveness or associated ecological factors in pastoral contexts. Currently, the management of Z. mauritiana is limited to the application of synthetic herbicides or mechanical clearing operations. There is also considerable interest in the exploitation of host-specific, natural enemies (biological control agents, herbivorous insects, fungi, bacteria, or viruses) for limiting the vigour, competitiveness, or reproductive capacity of Z. mauritiana in northern Australia. The development of a “bioherbicide” in lieu of synthetic counterparts may foster a more resilient coexistence between agricultural systems and the natural environment owing to its reduced environmental persistence and increased target specificity. This review summarises the current literature on the weediness, ecological impacts, and current management of this problematic weed, thereby identifying (i) opportunities for further research and (ii) recommendations for improved management within its invasive range.
Abstract The reproductive biology of the ovoviviparous peripatus Euperipatoides rowelli was investigated from field collections and laboratory cultures. The sexes have different demographics. The frequency distribution of individual weight is essentially L‐shaped in females, but closer to normality for males: thus the sexes must exhibit different patterns of growth and/or mortality. Males are generally much smaller and rarer than females. The primary sex ratio seems to be 1:1 with equal investment in the sexes, while the tertiary ratio is highly female‐biased. Logs with fewer individuals tend to be male‐biased while well‐populated logs tend to be female‐biased. Males mature at 15–30% of the bodyweight of mature females. The weight frequency distribution of males without developed sperm in their tracts is strongly skewed to the lower weights, while that of males with sperm is more normally distributed, indicating that sperm production occurs as soon in life as possible. Males mature in their first year of life, if growth rates in culture may be extrapolated to the wild. In contrast to this rapid maturity in males, females may mature as late as their second or third years. Most mature females, and many prior to maturity, carry sperm in their spermathecae. After maturity, there is an approximately linear relationship between body mass and number of developing embryos. Reproduction in E. rowelli is significantly seasonal despite high individual variance, with a major bout of parturition in November–December (summer). A female can harbour one developed and one undeveloped batch of embryos in each uterus. Excesses of developed embryos in one uterus are counterbalanced by deficits of undeveloped ones, indicating that females can use their paired reproductive tracts independently. Individual females in culture can experience episodes of parturition approx. 6 months apart without re‐mating, thus gestation may be 6 months or more. Sperm in spermathecae remain capable of vigorous swimming for at least 9.5 months.
results of diagnostic assays for ratoon stunting disease (RSD) at Harwood were analysed for the period between 2004 and 2011. Data recorded included variety and crop class, which ranged from plant crops after fallow or plough-out replant, up to 4th ratoons and older. There were significantly higher infection rates in replant versus fallowed crop classes. While RSD was detected in 9.4% of all prospective planting material, there were significant differences in infection levels among varieties, generally with higher levels of infection in varieties with higher susceptibility ratings. These results are discussed in relation to current RSD management strategies, the need for comprehensive susceptibility information and the role of resistant varieties.
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