Growth and Nutrition of Mollicute-Infected Maize

Maize bushy stunt phytoplasma (MBSP) and corn stunt spiroplasma (CSS) diseases are widespread in Brazil. The leafhopper Dalbulus maidis is the insect vector for these pathogenic mollicutes. The effects of these diseases on the development of maize plants and the possible interaction of soil water availability on these effects were evaluated in two experiments carried out on potted plants. Experiment 1 was carried out in a 2 × 4 factorial, where factor 1 corresponded to healthy and mollicute-infected plants and factor 2 to the maintenance of 40, 60, 80, and 100% of the total soil water availability. Leafhoppers collected from a field with high incidence of these diseases were used to inoculate plants with mollicutes. There were three treatments in experiment 2: healthy plants, plants infected with phytoplasma, and plants infected with spiroplasma. MBSP was predominant in experiment 1. The infected plants grew less and lowered nutrient uptake, in distinct proportions, indicating a differential effect of mollicutes on nutrient uptake independent of available soil water. Soil water availability did not significantly affect plant growth and nutrient uptake or mollicute infection. The results indicated that plants infected by mollicutes contained less protein than healthy plants. Experiment 2 showed a reduction in growth of plants infected with mollicutes and less nutrient uptake by spiroplasma-infected plants. The results showed a detrimental effect of the spiroplasma on Mg uptake. Both experiments showed more water retention by infected plants than by healthy ones. These experiments clearly demonstrated that reduced plant growth and nutrient uptake are major effects on plants infected with MBSP and CSS.

Aspectos da biologia da cigarrinha-do-milho, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae)

Na cultura do milho, a cigarrinha, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae) é vetora de três patógenos: Spiroplasma kunkelii (corn stunt spiroplasma), o fitoplasma do milho (maize bushy stunt phytoplasma) e o vírus da risca do milho (maize rayado fino vírus). Os prejuízos causados por essas doenças podem variar de nove a 90 %, dependendo da susceptibilidade das cultivares e dos patógenos envolvidos. O objetivo deste trabalho foi estudar aspectos da biologia de D. maidis, sob condições controladas e utilizando-se insetos e cultivares de milho e sorgo adaptados às condições brasileiras. Plântulas de milho e de sorgo foram cultivadas em vasos plásticos, cobertas com gaiolas de plástico e infestadas com 10 adultos por planta. Sempre utilizando-se 10 plântulas por tratamento, foram conduzidos dois ensaios independentes. No 1°, estudou-se o período de incubação nas temperaturas constantes de 17, 20, 23, 26, 29 e 32ºC ± 1ºC e fotofase de 12 h. No 2°, estudou-se o desenvolvimento de ninfas à temperatura constante de 26,5 ± 2ºC e mesma fotofase. O período de incubação foi mais curto nas temperaturas de 26 e 29ºC, nas quais cerca de 70% das ninfas levaram nove dias para a eclosão. Foram observados até cinco ínstares, embora cerca de 76% da população tenha completado o desenvolvimento passando por apenas quatro ínstares. A duração média de cada instar foi de 3,14 dias. Os adultos viveram em média 51,4 dias e o ciclo médio de ovo a adulto foi de 26,3 dias. Portanto, para a manutenção de colônias de insetos ou no desenvolvimento de estudos com essa espécie é importante observar os limites máximos e mínimos de temperatura.

EUDORYLAS (METADORYLAS) SP. (DIPTERA: PIPUNCULIDAE): A PREVIOUSLY UNREPORTED PARASITOID OF DALBULUS MAIDIS (DELONG AND WOLCOTT) AND DALBULUS ELIMATUS (BALL) (HOMOPTERA: CICADELLIDAE)

The genus Dalbulus (Homoptera: Cicadellidae) consists of 11 species, 10 of which can be found in México (Nault 1990). Some members in the genus, such as the corn leafhopper, Dalbulus maidis (DeLong and Wolcott), and the Mexican corn leafhopper, Dalbulus elimatus (Ball) are serious pests of maize due to their transmission of three corn stunting pathogens: corn stunt spiroplasma (CSS; Spiroplasma kunkelii Whitcomb et al.), maize bushy stunt mycoplasmalike organism (MBSM), and maize rayado fino virus (MRFV) (Nault 1990). Due to the widespread damage that these leafhopper-vectored pathogens cause in maize-growing regions in Latin America, a search for the leafhopper natural enemies was conducted in maize agroecosystems in central México.

Serum-free media for cultivation of spiroplasmas

Serum-free media that contained bovine serum albumin and lipids (fatty acids, cholesterol, phosphatidic acid, and phospholipids) to replace serum were formulated for the culture of some fastidious strains of corn stunt spiroplasma, Spiroplasma kunkelii. These media also supported good growth of other spiroplasmas, including epiphytic, entomopathogenic, and phytopathogenic strains. The growth rates attained in these serum-free media were comparable to those in media which contained serum. The serum-free broth and agar media were of major importance for culture of several fastidious strains of corn stunt spiroplasma because the serum-containing media supported little, if any, of their growth. Colonies of these fastidious strains were readily formed on serum-free agar media in aerobic, candle jar, and anaerobic environments, but were not readily formed on the serum-containing media. The serum-free media were less subject to deterioration during storage or incubation, and the growth-supporting capacity of serum-free media diminished more slowly than that of serum-containing media.Key words: Spiroplasma kunkelii, Spiroplasma citri, Mollicutes, Mycoplasma spp. culture, entomopathogens.

Defects of helicity and motility in the corn stunt spiroplasma, Spiroplasma kunkelii

Serum-free medium LD59 was used for primary isolation of Spiroplasma kunkelii (corn stunt spiroplasma) from diseased corn plants from Mississippi. Several strains were cloned in triplicate from one primary pure culture. Some of the strains were helical in cell shape, some were nonhelical, and some were partially helical, consisting of helical and nonhelical regions in the same cell. All helical strains except one (strain I-15) exhibited flexional and rotational motility in broth culture. Partially helical strains exhibited rotational movement in helical regions only. Nonhelical cells exhibited only flexional motility. These three morphological types produced three colony types on medium LD59 solidified with 0.8% agar. Nonhelical strains produced minute "fried egg" colonies (≤ 0.2 mm in diameter after 20 days incubation), while partially helical strains produced small colonies with granular centers surrounded by satellite colonies. Strains with normal helicity in general produced large, uniformly diffuse colonies (up to 2 mm), but one helical strain (I-15) appeared to be nonmotile in broth culture and to exhibit little translational motility in agar medium, accounting for development of minute granular colonies (about 0.2 mm in diameter). All new strains were serologically closely related to known strains of S. kunkelii, but polyacrylamide gel electrophoresis analysis of membrane proteins revealed minor differences. This is the first report of nonhelical strains of S. kunkelii and of helical strains with apparent impairment in translational motility.Key words: Spiroplasma kunkelii, nonhelical spiroplasmas, Mollicutes.