Virus-free garlic plants, when planted in the field, are quickly infected by viruses, but it is not known to what extent this affects the yield over successive crop cycles. The yield loss curve was studied for these plants during 5 years of tests in the field. Highly significant differences were detected in the weight and perimeter of bulbs in relation to the years of exposure to virus infection. An increase was observed in yield compared with chronically diseased plants of between 66 and 216% in weight and 13 and 37% in perimeter of bulbs in the first crop cycle and 49% in weight and 16% in perimeter in the fifth year. These results showed a gradual loss in yield until the third year, and subsequently the production values remained steady for the fourth and fifth years of testing but were still higher than those reached by chronically diseased plants.

Virus infection in garlic considerably reduces yield and quality in Argentina. The production of virus free “seed” was attempted by means of thermotherapy and meristem tip culture. A hot water treatment was employed to determine the lethal temperature/time combination for clonal type (c.t.) Blanco cloves. It was established that 50°C × 20 min, 50°C × 15 min and 55°C × 5 min were the limit thermal/time combinations which garlic could withstand. Those treatments were employed followed by meristem tip culture, however, none of the successfully developed plants after culture (only 13 %) were virus‐free. Hot air treatments in a growth chamber at 36°C lasting for 30, 40 and 60 days, and at 25°–32° for 30 days in a greenhouse were tested on c.t. Blanco. Cloves kept at room temperature throughout the experiment were employed as controls. In the 25°–32°C treatment, 73% of meristems produced plants and, of these, 33 % were virus free. After 30 and 40 days at 36 °C, 62 % and 67 % of the meristems developed into plantlets, of which respectively 51 % and 50 % were virus‐free. Very few meristems (10 %) developed into plants when cloves had been kept at 36°C for 60 days but the resulting plantlets were all virus free. Controls produced 78 % of plants, of which 14 % were virus free. Results of hot air treatments of 36 °C for 40 days performed on c.t. Colorado, Rosado, Paraguayo, Espaol and Hilario Ascasubi were similar to those obtained with c.t. Blanco. In Espaol and Hilario Ascasubi, no virus‐free plants were detected among control specimens (no thermotherapy treatment). The only virus (from up to 3 that infected the plants) that persisted in some plants after themotherapy and meristem tip culture was garlic yellow streak.

Garlic (Allium sativum) is infected by numerous viruses forming a viral-complex, which is widely distributed in the garlic production regions of Argentina. This work is the first report of the effect of two Allexivirus isolates, Garlic virus A (GarV-A) and Garlic virus C (GarV-C), on garlic yield. Garlic cvs. Morado-INTA and Blanco-IFFIVE were used in the experiments, and four treatments were evaluated: plants inoculated with GarV-A only, GarV-C only, virus-free plants (negative control), and plants infected with the virus-complex. Assays were performed in anti-aphid cages and in the field during 2002 and 2003. GarV-A caused significant reductions in bulb weight (14 to 32%) and diameter (6 to 11%) compared with the negative control in the two cultivars under both assay conditions. GarV-C caused less damage than GarV-A (15% in weight and 5% in diameter) with respect to the negative control in cv. Blanco-IFFIVE, and did not produce significant yield losses in cv. Morado-INTA in either year or under either assay condition.

Garlic plants (Allium sativum) are naturally infected by a complex of viruses in the genera Potyvirus, Carlavirus, and Allexivirus. The yield of virus-free garlic plants (noninoculated control) was compared with that of plants infected with an Argentinean isolate of Leek yellow stripe virus (LYSV; L treatment) and garlic plants infected with the virus complex (VC). Evaluations were conducted in the field and in anti-aphid cages during two crop cycles after planting three sizes of cloves (categories). The percent plant emergence in the noninoculated control and in the L treatments (between 80 and 100%) did not differ statistically, but the percent emergence for these two treatments was double that for the VC treatment (25 to 62%). Plant height and leaf number in the L treatment were lower than in the noninoculated control during the first evaluation (year 1), but they did not differ during the second evaluation (year 2). However, both treatments produced taller plants with more leaves than those of VC in both years. The L treatment decreased bulb weight up to 28% and perimeter up to 9% when compared with those in the noninoculated control maintained in the anti-aphid cages until the end of the experiment. However, differences between these treatments were higher in the field experiments where plants were exposed to infection by other viruses (up to 36% in bulb weight and 13% in perimeter). Bulbs of the VC-infected plant treatment were reduced up to 74% in weight and 37% in perimeter. In field evaluations, a high percentage of plants were infected with Onion yellow dwarf virus (58 to 100%), whereas fewer were infected with LYSV (15 to 68%). Garlic virus A infection was high in plants previously infected with LYSV (96 and 97%), but lower in the noninoculated control (12 and 68%). These results show the high impact of the virus complex on garlic yield and the effect of LYSV as a component of the garlic virus complex.