Probing behavior of the corn leafhopper Dalbulus maidis on susceptible and resistant maize hybrids

The corn leafhopper Dalbulus maidis is the main vector of the pathogens that cause corn stunt, a major disease of maize in the Americas. As host resistance is an efficient tool to control diseases, the findings of a previous report showed that some corn hybrids are resistant to D . maidis . In this work, we assessed the probing behavior of D . maidis on susceptible and resistant corn hybrids using EPG (Electrical Penetration Graph) technology. Fifteen-day-old females were monitored for 20 hours, with access to hybrids DK390, DK670, DK79-10, and DK72-10. Hybrids DK390 and DK72-10 showed resistance to D . maidis in phloem, since insects feeding on these hybrids presented more salivation events in phloem without subsequent ingestion, which are seen as failed attempts to ingest. A reduction of the total duration of phloem ingestion was observed, and accordingly of the time spent by insects with access to these hybrids on xylem ingestion. The hybrid DK390 also had mesophyll resistance, seen as less probing time and a higher number of probes of short duration. These findings support and are consistent with previous research, providing useful information to characterize maize hybrids resistant to D . maidis , and so to corn stunt.

Corn Stunt Disease: An Ideal Insect–Microbial–Plant Pathosystem for Comprehensive Studies of Vector-Borne Plant Diseases of Corn

Over 700 plant diseases identified as vector-borne negatively impact plant health and food security globally. The pest control of vector-borne diseases in agricultural settings is in urgent need of more effective tools. Ongoing research in genetics, molecular biology, physiology, and vector behavior has begun to unravel new insights into the transmission of phytopathogens by their insect vectors. However, the intricate mechanisms involved in phytopathogen transmission for certain pathosystems warrant further investigation. In this review, we propose the corn stunt pathosystem (Zea mays–Spiroplasma kunkelii–Dalbulus maidis) as an ideal model for dissecting the molecular determinants and mechanisms underpinning the persistent transmission of a mollicute by its specialist insect vector to an economically important monocotyledonous crop. Corn stunt is the most important disease of corn in the Americas and the Caribbean, where it causes the severe stunting of corn plants and can result in up to 100% yield loss. A comprehensive study of the corn stunt disease system will pave the way for the discovery of novel molecular targets for genetic pest control targeting either the insect vector or the phytopathogen.

Characterization of Components of Resistance to Corn Stunt Disease

Considering the occasional but increasing presence of corn stunt disease in the subtropical region of Argentina, the objective of this research was to devise an effective strategy to screen disease-resistant genotypes in the absence of high and constant natural pressures. To do so, the presence of antixenosis and antibiosis as components of resistance to vector Dalbulus maidis (DeLong 1923) as well as resistance to the pathogen Spiroplasma kunkelii (Whitcomb et al. 1986) under artificial inoculation conditions were investigated in four widely-distributed maize hybrids in Argentina. The hybrids shown differences in the levels of resistance and target organisms (either the insect vector or the pathogen). Antixenosis and antibiosis to D. maidis were observed in DK72-10. Resistance of DK79-10 to S. kunkelii was evidenced by a delayed onset of symptoms, and DKB390 was antixenotic to D. maidis and highly resistant to S. kunkelii. A good association was found between symptom severity and yield, but not between symptom severity and accumulation of pathogen S. kunkelii. In conclusion, the proposed methodology was efficacious and can aid the screening of resistant genotypes in breeding programs to reduce the impact of corn stunt disease, ensuring that hybrids with good resistance level will be planted by farmers whenever disease occurs.

Incidence of corn stunt disease in off-season corn hybrids in different sowing seasons

The objective of this work was to evaluate the incidence of corn stunt disease and its effects on the grain yield of off-season corn (Zea mays) hybrids in different sowing seasons. The experiment was conducted in three sites in the state of Tocantins, in different sowing seasons, in a randomized complete block design, with 30 hybrids (treatments) and three replicates. Corn stunt disease incidence was assessed at 80 days after emergence, varying between hybrids and sowing seasons, with a marked effect of sowing season. The most resistant hybrids were: MG652 PW, Penta VIP, MG600 PW, NS90 PRO2, LG3040 VIP3, MG580 PW, and Defender VIP. The Fórmula VIP2 hybrid was the most susceptible to corn stunt disease. The incidence of the disease increased in the later sowing seasons, causing significant declines in grain yield. The most productive hybrids were: MG580 PW, SYN 5T78 VIP, 2B810 PRO, MG600 PW, Supremo VIP, 2B512 PW, NS92 PRO2, P30S31 VYH, MG652 PW, Penta VIP, SX5371 VIP3, and LG6036 PRO. Corn hybrids vary greatly in their resistance to corn stunt disease, and, the later the sowing season, the higher the disease incidence and the lower the grain yield.

Evaluación de líneas S1 derivadas de la población 73 del tercer ciclo de mejoramiento para resistencia al achaparramiento

The presence of endophytic maize stunt in the pacific coastal plain and other drier parts of Nicaragua, represents a major problem relative to maize grain production. To reduce the risk of losses and to secure sustainable production for maize in this extensive production region, the development of cultivars with resistance to this disease is necessary. With the objective of identifying and selecting germplasm with genetic resistance to this disease, 400 S1 lines were evaluated during the cycle where the disease is more prevalent (August through December). These lines were derived from population 73 out of the third cycle of recurrent selection. The trial was planted at the experimcnt station of thc Centro Nacional de Granos Basicos at Managua, Nicaragua, where a 20 x 20 lattice design was used with two replications. The selected fraction to be recombined for the second cyclc outyielded thc population mean yield by 58%, in stunt free plants by 52 %, and stunt free ears by 64 %. These observcd levels were superior to the local check, the tolerant variety NB- 6. The results obtained indicate that significant advances havc been obtained in breeding efforts for resistance to corn stunt.

Complete Genome Sequence of Spiroplasma kunkelii Strain CR2-3x, Causal Agent of Corn Stunt Disease in Zea mays L.

Spiroplasma kunkelii causes corn stunt disease of Zea mays L. in the Americas. Here, we report the nucleotide sequence of the 1,463,926-bp circular chromosome and four plasmids of strain CR2-3x. This information will facilitate studies of Spiroplasma pathogenicity and evolutionary adaptations to transkingdom parasitism in plants and insect vectors.