“Peste negra” is a disease, caused by tospoviruses, that affects tomato crops in Argentina. Knowledge of the diversity, frequency, and distribution of different tospoviruses is essential for developing a rational control program based on genetic resistance sources. A study of the geographical distribution of tospoviruses affecting tomato crops in Argentina is presented in this paper. The areas surveyed were between the Tropic of Capricorn and 40°S and between longitude 58°W and 70°W. Tospovirus species were identified through double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), using polyclonal antisera against Tomato spotted wilt virus (TSWV), Groundnut ringspot virus (GRSV), and Tomato chlorotic spot virus (TCSV). From tomato samples that reacted positively with any of the used antisera, 63% were GRSV, 28.2% were TCSV, and 8.8% were TSWV. A differential geographical distribution of tospoviruses was determined. Every plant that tested positive for GRSV was from central and northwest Argentina, while every plant TCSV-positive was from the northeast. TSWV was found only in the Río Negro Valley region in the south of the country. The wide dispersion of GRSV may be related to the spread of Frankliniella shultzei, which transmits this virus more efficiently than other vectors.

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Chlorotic dwarf (CD), the most important disease in the sweet potato-producing regions of Argentina, is caused by the synergistic combination of two aphid-transmitted potyviruses with a whitefly-transmitted crinivirus. Sweet potato feathery mottle virus, sweet potato mild speckling virus, and a crinivirus (serologically related to sweet potato chlorotic stunt virus) were associated with CD. The synergistic combination of these three viruses reproduced the disease.

Buffel grass (Cenchrus ciliaris L.) is an important apomictic grass used as forage for ruminant livestock. Biotechnological methods provide opportunities for producing new germplasm. Mature embryos of fourteen buffel grass apomictic cultivars (2n = 4x = 36) were used to induce embryogenic callus formation using a basal medium supplemented with 3% sucrose and with the testing of five concentrations of 2,4‐dichlorophenoxyacetic acid (2,4‐D) and four concentrations of 6‐benzylaminopurine (BAP). The effects of cultivar and culture medium on callus induction and plant regeneration were evaluated. Significant differences were observed among the fourteen cultivars and the five concentrations of 2,4‐D (P < 0·01). Values for embryogenic callus production varied from 0 to 86·7. Most cultivars showed the highest level of embryogenic callus production on the medium with the concentration of 3 mg L−1 2,4‐D. The addition of different BAP concentrations in combination with 2,4‐D in the medium inhibited embryogenic callus growth and did not permit plant regeneration. The data clearly demonstrated that the genotype and concentrations of 2,4‐D had significant effects both on the frequency of embryonic callus formation from mature embryos and on the subsequent efficiency of plant regeneration of apomictic cultivars of buffel grass. Cultivars Biloela and Nunbank showed the greatest efficiency in in vitro culture response.