Sorghum insect problems and management

Optimizing Soil Health and Sorghum Productivity through Crop Rotation with Quinoa

Crop rotation has been considered a potential solution to mitigate the negative effects of the continuous cropping of sorghum, including soil quality issues, inadequate plant development, and diminished yield and quality. A two-year field experiment was conducted to compare the effects of sorghum-sorghum continuous cropping and quinoa-sorghum rotation on soil properties and sorghum yield. The treatments were arranged in a randomized complete block design with three replicates. Sorghum seeds (Jinza 22) and quinoa seeds ('Jiaqi 1' variety) were used. Soil samples were collected before and during the experiment for the analysis of physicochemical properties. The yield traits of sorghum were measured at maturity. The results showed that soil nutrients and organic matter were higher in the top 0-20 cm soil depth compared to 20-40 cm depth, with significant differences observed between cropping systems. Sorghum-quinoa cropping increased soil total N and organic matter, particularly at the jointing and maturity stages of sorghum. However, the available phosphorus was higher under continuous cropping at all growth stages. Crop rotation significantly improved sorghum yield traits, including spike fresh weight, spike dry weight, grain weight per spike, and grain yield per hectare. A correlation analysis revealed positive relationships between soil total N, organic matter, and sorghum yield. Overall, sorghum-quinoa rotation demonstrated potential for improving soil fertility and enhancing crop productivity compared to continuous cropping, although further studies are needed to explore the long-term effects and optimize management practices.

The Characterization of Melanaphis sacchari Microbiota and Antibiotic Treatment Effect on Insects

Insects are under constant selective pressure, which has resulted in adaptations to novel niches such as crops. This is the case of the pest Melanaphis sacchari, the sugarcane aphid, native to Africa and currently spreading worldwide. The aphid undergoes successful parthenogenesis, causing important damage to a variety of crops and leading to important economic losses for farmers. A natural M. sacchari population grown in sorghum was studied to identify its microbiome through the sequencing of its 16S rDNA metagenome. A high proportion of Proteobacteria, followed by Firmicutes, Bacteroidetes, and Actinobacteria, was observed. We also detected Wolbachia, which correlates with the asexual reproduction of its host. M. sacchari was challenged in a bioassay with the antibiotics oxytetracycline and streptomycin, resulting in a dose-dependent decay of its survival rate. The possibility of controlling this pest by altering its microbiota is proposed.

Sorghum defense responses to sequential attack by insect herbivores of different feeding guilds

MAIN CONCLUSION

Insect herbivores of different feeding guilds induced sorghum defenses through differential mechanisms, regardless of the order of herbivore arrival on sorghum plants. Sorghum, one of the world's most important cereal crops, suffers severe yield losses due to attack by insects of different feeding guilds. In most instances, the emergence of these pests are not secluded incidents and are followed by another or can also co-infest host plants. Sugarcane aphid (SCA) and fall armyworm (FAW) are the two most important destructive pests of sorghum, which belongs to sap-sucking and chewing feeding guilds, respectively. While the order of the herbivore arriving on the plants has been found to alter the defense response to subsequent herbivores, this is seldom studied with herbivores from different feeding guilds. In this study, we investigated the effects of sequential herbivory of FAW and SCA on sorghum defense responses and their underlying mechanism(s). Sequential feeding on the sorghum RTx430 genotype by either FAW primed-SCA or SCA primed-FAW were monitored to unravel the mechanisms underlying defense priming, and its mode of action. Regardless of the order of herbivore arrival on sorghum RTx430 plants, significant defense induction was observed in the primed state compared to the non-primed condition, irrespective of their feeding guild. Additionally, gene expression and secondary metabolite analysis revealed differential modulation of the phenylpropanoid pathway upon insect attack by different feeding guilds. Our findings suggest that priming in sorghum plants upon sequential herbivory induces defense by the accumulation of the total flavonoids and lignin/salicylic acid in FAW primed-SCA and SCA primed-FAW interaction, respectively.

Recent advancements in the breeding of sorghum crop: current status and future strategies for marker-assisted breeding

Sorghum is emerging as a model crop for functional genetics and genomics of tropical grasses with abundant uses, including food, feed, and fuel, among others. It is currently the fifth most significant primary cereal crop. Crops are subjected to various biotic and abiotic stresses, which negatively impact on agricultural production. Developing high-yielding, disease-resistant, and climate-resilient cultivars can be achieved through marker-assisted breeding. Such selection has considerably reduced the time to market new crop varieties adapted to challenging conditions. In the recent years, extensive knowledge was gained about genetic markers. We are providing an overview of current advances in sorghum breeding initiatives, with a special focus on early breeders who may not be familiar with DNA markers. Advancements in molecular plant breeding, genetics, genomics selection, and genome editing have contributed to a thorough understanding of DNA markers, provided various proofs of the genetic variety accessible in crop plants, and have substantially enhanced plant breeding technologies. Marker-assisted selection has accelerated and precised the plant breeding process, empowering plant breeders all around the world.

Behavioral mechanism of transfer and dispersal of Propylaea japonica in cotton adjacent to sorghum fields

Increasing crop biodiversity, such as by adjacent managed crops, is recognized as an effective biological control measure. However, few studies have focused on the mechanisms involved in how adjacent managed crops increase natural enemy populations, leading to reduced pest numbers. This study investigated the hypothesis that cotton grown adjacent to sorghum would positively influence the feeding and oviposition preferences of the ladybug Propylaea japonica, which predates cotton aphids, leading to enhanced pest control. The populations of Aphis gossypii were significantly lower and those of P. japonica were significantly higher in cotton grown adjacent to sorghum compared with monoculture cotton fields. Regardless of diet on which the larva of P. japonica were reared (Melanaphis sacchari, A. gossypii, and 50% M. sacchari + 50% A. gossypii), the adults always consumed significantly more M. sacchari compared with A. gossypii. P. japonica also showed significantly higher feeding and oviposition preferences for host plants bearing aphids to only host plants. P. japonica fed M. sacchari preferred to lay eggs on cotton, whereas those fed A. gossypii preferred to lay eggs on sorghum. These results suggest that the habitat of natural enemies can be expanded by influencing their feeding and oviposition preferences to achieve pest control in adjacent cropping systems. This research, which incorporates field and laboratory studies, suggests an approach for the successful conservation and biological control of cotton aphids using adjacent managed cotton and sorghum crops.

Greenbug feeding-induced resistance to sugarcane aphids in sorghum

Plants are attacked by multiple insect pest species and insect herbivory can alter plant defense mechanisms. The plant defense responses to a specific herbivore may also contribute to the herbivore growth/survival on plants. Feeding by one insect species can modulate the plant defenses, which can either facilitate or hamper the colonization of subsequent incoming insects. However, little is known about the effect of sequential herbivory on sorghum plants. In this study, we demonstrate that a specialist aphid, sugarcane aphid (SCA; Melanaphis sacchari) grows faster on sorghum than a generalist aphid species, greenbug (GB; Schizaphis graminum). We also determined how the pre-infestation of SCA on sorghum affected the invasion of GB and vice-versa. Our sequential herbivory experiments revealed that SCA reproduction was lower on GB-primed sorghum plants, however, the reverse was not true. To assess the differences in plant defenses induced by specialist vs. generalist aphids, we monitored the expression of salicylic acid (SA) and jasmonic acid (JA) marker genes, and flavonoid biosynthetic pathway genes after 48 h of aphid infestation. The results indicated that GB infestation induced higher expression of SA and JA-related genes, and flavonoid pathway genes (DFR, FNR, and FNSII) compared to SCA infestation. Overall, our results suggested that GB-infested plants activate the plant defenses via phytohormones and flavonoids at early time points and hampers the colonization of incoming SCA, as well as explain the reproductive success of SCA compared to GB.

Molecular and morphological evidence for resistance to sugarcane aphid (Melanaphis sacchari) in sweet sorghum [Sorghum bicolor (L.) Moench]

Aphids are one of the devastating pests affecting the productivity of sorghum in many countries. The aim of the present investigation was to identify sweet sorghum genotypes resistant to the sugarcane aphid, Melanaphis sacchari (Zehntner). A Sequence Characterized Amplified Region (SCAR) marker linked to an aphid-resistance gene (RMES1) was first used to prescreen for resistant genotypes in 561 sorghum accessions. Molecular assays indicated that 91 sorghum accessions in the collection had the RMES1 resistance marker allele. Of those, 26 agronomically superior sweet sorghum accessions, along with three commercial cultivars and one susceptible check, were further evaluated in two locations (Antalya, a lowland province, and Konya, a highland province) under field conditions. These accessions were scored for resistance to aphid damage under natural aphid infestations. The number of aphids counted on the plant leaves and stalks in the accessions during the growing seasons was used to score resistant genotypes on a scale of 1-5, where 1 was highly resistant (plants having 0-50 aphids/plant) and 5 was highly sensitive (plants having 1000 + aphids/plant). Fumagine intensity on the leaves was also taken into consideration. Ten accessions from the lowland and one accession from the highland scored "1," indicating a high resistance to aphid infestation. A further 13 accessions scored "1" or "2" in both environments. Only two accessions scored "4," and no accession scored "5," indicating the utility of the RMES1 marker for prescreening purposes. One accession, BSS507, showed outstanding resistance to M. sacchari, with a score of "1" in both environments.

Invasion of sorghum in the Americas by a new sugarcane aphid (Melanaphis sacchari) superclone

In the United States (US), the sugarcane aphid (SCA) Melanaphis sacchari (Zehnter) (Hemiptera: Aphididae) was introduced in the 1970s, however at that time it was only considered a pest of sugarcane. In 2013, a massive outbreak of M. sacchari occured on sorghum, resulting in significant economic damage to sorghum grown in North America including the US, Mexico, and Puerto Rico. The aim of the present study was to determine if the SCA pest emergence in American sorghum resulted from the introduction of new genotypes. To this end we used microsatellite markers and COI sequencing to compare the genetic diversity of SCA populations collected in the Americas after the 2013 SCA outbreak on sorghum (during 2013–2017) to older samples collected before the pest outbreak (during 2007–2009). Our results show that the SCA outbreak in the Americas and the Caribbean observed since 2013 belong to populations exhibiting low genetic diversity and consisting of a dominant clonal lineage, MLL-F, which colonizes Sorghum spp. and sugarcane. The comparison of MLL-F specimens collected post-2013 with specimens collected in Louisiana in 2007 revealed that both populations are genetically distinct, according to COI sequencing and microsatellite data analyses. Our result suggest that MLL-F is a new invasive genotype introduced into the Americas that has spread rapidly across sorghum growing regions in the US, Mexico, Honduras and the Caribbean. The origin of this introduction is either Africa or Asia, with Asia being the most probable source.