Introduction

Potato virus Y (PVY) is the type species of the Potyvirus genus, one of the genera in the Potyviridae family, which includes some of the most destructive plant viruses (^{Kerlan, 2006}; ^{Scholthof et al., 2011}; ICTV, 2022). PVY ranks fifth among the ten most important plant viruses worldwide (Scholthof et al., 2011) and is considered the most economically significant and devastating viral disease affecting potato crops (Solanum tuberosum) (^{Shukla et al., 1998}; ^{Singh et al., 2008}; ^{Gray et al., 2010}; ^{Karasev and Gray, 2013}; ^{Quenouille et al., 2013}).

This virus has been a persistent issue in potato production (^{Lacroix et al., 2010}; ^{Kostiw, 2011}), as it affects commercial production crops and is among the three most critical diseases in seed potato production (NOM-041-FITO-2002). High PVY incidence levels have been responsible for the disqualification of seed lots for certification, leading to a significant reduction in crop value and, in some cases, a shortage of certified seed (^{Gray et al., 2010}).

In Mexico, the use of certified seed tubers for potato production is a phytosanitary requirement established by the Official Mexican Standards NOM-040-FITO-2002 and NOM-041-FITO-2002. However, the yield benefits of using certified seed free of rapidly spreading viruses, such as PVY, have not been evaluated. Additionally, there are no reports estimating yield and economic losses caused by this virus in the potato-producing region of Coahuila. Consequently, the objectives of this research were: 1) to experimentally evaluate the losses caused by PVY in Fianna potato plants; and 2) to estimate the yield and economic losses caused by PVY in the potato-producing region of Coahuila.

Materials and Methods

Study Sites. The experimental plot used to evaluate losses caused by PVY in 2022 was located at the “El Bajío” Experimental Field of the Universidad Autónoma Agraria Antonio Narro (UAAAN), situated at 25° 21’ 21” N and 101° 02’ 26” W. The field was plowed and furrowed with an 80 cm spacing between furrows and a bed width of 80 cm. Additionally, during the same year, foliage samples were collected from four commercial Fianna potato fields, conventionally managed by their owners. These production fields were located in the Emiliano Zapata and Huachichil ejidos in Arteaga, Coahuila, at 25° 06’ 00” N and 100° 45’ 14” W and

25° 12’ 15” N and 100° 47’ 34” W, respectively.

PVY Diagnostic Method. Two PVY diagnostic methods were used, both based on the antigen-antibody reaction: the ImmunoStrips® method (AGDIA, 2023) and the

double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) method (^{Engvall and Perlmann, 1971}).

Obtaining propagative material. During the 2021 potato harvest in the production regions of Coahuila and Nuevo León, Mexico, 250 Fianna tubers were collected. The tubers were kept under laboratory conditions until two sprouts, 2 to 7 cm in length, developed on each. Composite samples were formed by mixing five sprouts from different tubers, and the presence or absence of PVY was determined in each composite sample using ImmunoStrips® (AGDIA, 2023). The tubers were classified based on the results: those testing positive for PVY and those without the virus. Two groups were then formed from this classification. Each group included both PVY-positive and PVY-negative tubers. The first group was designated for seedling production, while the second was used as seed tubers. The tubers intended for seedling production were planted in 5 kg polyethylene bags under greenhouse conditions (22 to 26 °C) and covered with insect-proof netting. Fifteen days after plant germination, foliage samples (three leaflets per plant) were collected and individually diagnosed for PVY using the DAS-ELISA method with AGDIA kits. PVY-infected plants were kept separate from healthy plants until field transplantation (Trial 1). Tubers used as seed were individually tested for PVY using the same method applied to seedlings. PVY-infected tubers were separated from healthy ones and later planted at the “El Bajío” Experimental Field (Trial 2).

Results and Discussion

Assay 1 - Transplantation. The yield in furrows transplanted with infected seedlings was 0.4 kg/plant, lower than the 0.57 kg/plant observed in furrows transplanted with healthy seedlings. Based on these data, the yield per hectare was 22.22 t for seedlings derived from infected seed tubers and 31.66 t for those from healthy seed tubers (Figure 1). Using this information, it was calculated that the yield loss due to secondary PVY infections in transplanted plants within the experimental plot was 30%. Although plant and tuber size were not evaluated in this assay, all furrows showed reduced growth in PVY-infected plants (Figure 2). These infected plants produced fewer and smaller tubers compared to virus-free plants.

Figure 1 Yield per hectare of Fianna potato plants in Assay 1. 

Figure 2 Left: plants grown from tuber seed infected with PVY; right: plants grown from PVY-free tuber seed. 

Assay 2 - Direct sowing. The yield of plants grown from PVY-infected seed tubers was 0.55 kg/plant, significantly lower than the 1.17 kg/plant recorded for healthy plants. Based on these results, the yield per hectare was 30.72 t for infected seed tubers and 64.84 t for healthy seed tubers (Figure 3). Using these data, it was calculated that the yield loss due to secondary PVY infections in the experimental plot was 53% (Figure 4). Plants developed from PVY-infected seed tubers produced

Figure 3 Yield per hectare of plants grown from infected tuber seed (0), plants inoculated at 20, 40, 60, and 80 DAE, and healthy plants (remained healthy throughout the 120-day cycle). 

Figure 4 Fit of the Berger model explaining 98% of the variation in losses relative to the date of PVY infection (days after emergence - DAE). 

fewer tubers of lower quality compared to healthy plants. The number of “first quality” and “second quality” tubers was higher in healthy plants than in infected ones (Figures 5 and 6).

Figure 5 Quantity and quality of tubers produced by plants grown from infected tuber seed (0), plants inoculated at 20, 40, 60, and 80 days after emergence (DAE), and healthy plants. 

Plants inoculated at 20, 40, 60, and 80 days after emergence (DAE) yielded

0.81, 0.97, 1.06, and 1.16 kg/plant, respectively. Correspondingly, the calculated yield per hectare for these inoculation times was 44.88, 53.65, 58.68, and 64.44 t (Figure 3). These results indicate that primary PVY infections caused yield losses of 30.7%, 17.3%, 9.5%, and 0.61%, depending on the timing of inoculation (Figure

4). Plants inoculated at 20, 40, and 60 DAE produced higher-quality tubers than those grown from infected seed tubers, including “first quality” tubers and a greater number of “second quality” and “third quality” tubers. However, both the quantity and quality of tubers from plants inoculated at these earlier times were lower than those of plants inoculated at 80 DAE and healthy plants (Figures 5 and 6).

A decrease in yield losses was observed as the age of the plant at the time of PVY infection increased. Using this relationship between the age of the plant at infection and yield loss, it was determined that the model that best describes this

relationship is the Berger model: Y=1/1+e-lny01-y0+r*dae. (Figure 6). This conclusion is supported by the coefficient of determination (R²) and the

high significance of the regression when applying this model.

Figure 6 Tubers produced by: A) plants grown from infected tuber seed; B) plants inoculated at 20 DAE; C) plants inoculated at 40 DAE; D) plants inoculated at 60 DAE; E) plants inoculated at 80 DAE; F) healthy plants (no inoculation). 

Estimation of losses in commercial plots. The percentage of infected plants in the commercial plots ranged from 0% to 100% across the four samplings. In Emiliano Zapata, the incidence was 100% in the first three samplings and 92% in the fourth. In San Felipe and La Mesa, the percentages were 100% and 5%, respectively. No presence of PVY was detected in Huachichil (Table 1).

Using the loss estimation model Y = 1/[1 + e (-{ln[0.67205626] + - 0.0694 * dae})], developed with data from the two experimental plot assays and the percentage of infected plants at various crop ages in the commercial plots, yield and economic losses were estimated for the potato-producing region of Coahuila (Table 2). Considering that the sampled area (200 plants) represents 77% of the total area planted with the Fianna variety in the state and using the average price per ton of $10,000 (SIAP, 2022), it was estimated that the state-wide yield loss is 18%. This corresponds to an economic loss of $19,068,500 for the state.

Losses from primary infections. The yield of plants inoculated at 20, 40, and 60 DAE was lower compared to those inoculated at 80 DAE and the control (healthy plants), with the latter two showing similar yields. This could be attributed to the limited time available for the virus to replicate and disrupt the plant’s physiological system, resulting in no significant reduction in productivity. ^{Hernández (2006}) reported yield reductions of 28.5% and 20.7% when inoculating Atlantic potato plants at 20 and 60 DAE under greenhouse conditions. A similar pattern was observed in this study, where plants inoculated at 20 and 60 DAE exhibited yield reductions of 30.7% and 9.5%, respectively.

Losses from secondary infections. Secondary PVY infections transmitted through seed tubers caused yield losses of 30% and 53% compared to plants grown from virus-free seed tubers. These findings align with those reported by ^{Hane and Hamm (1999}), who found total yield reductions of 29% to 79% depending on the potato variety. Similarly, they are consistent with the study by ^{Whitworth et al. (2006}), which reported total yield reductions ranging from 38% to 63%, influenced by soil nitrogen levels and potato variety. The results highlight the critical importance of seed tuber condition in potato production. Yield was significantly lower when seed tubers were infected compared to virus-free tubers. Thus, one of the most effective ways to avoid yield losses is to plant certified virus-free seed tubers. Certification programs should also implement stricter regulations to prevent the sale of contaminated seed tubers. These findings support the conclusions of ^{Gray et al. (2010}) and ^{Vreugdenhil et al. (2007}), who emphasized that PVY is one of the main contributors to reduced potato yield and quality. In the United States, PVY has also led to a shortage of certified virus-free seed tubers due to the rejection of contaminated lots, resulting in a significant decrease in crop value (Gray et al., 2010).

Tuber quantity and quality. Plants infected through seed tubers produced fewer and smaller tubers compared to those grown from virus-free seed tubers. Similarly, plants inoculated at 20, 40, and 60 days after emergence (DAE) showed lower tuber yield and quality than plants inoculated at 80 DAE and those from healthy seed tubers. These findings align with the reports of ^{Bokx (1980}), ^{Salazar (1995}), ^{Vreugdenhil et al. (2007}), and ^{Nolte et al. (2009}), who noted that PVY disrupts the plant’s physiological processes at an early stage, impairing photosynthesis and carbohydrate accumulation. This results in stunted plant growth and reduced tuber production. Yield losses caused by PVY in the two experimental plot assays ranged from 9.4% to 53%, consistent with previous reports. Authors such as ^{Beczner et al. (1984}), ^{Hane and Hamm (1999}), ^{Pérez et al. (2004}), Salazar (1995), ^{Whitworth et al. (2006}), and ^{Zuñiga et al. (1999}) have reported that PVY-related losses in

potato crops vary between 10% and 80%, depending on the cultivar, viral strain characteristics, storage conditions, environmental factors, and the management of insect pests and weeds.

Estimation of losses in Coahuila. The commercial fields with the highest percentage of infected plants were San Felipe and Emiliano Zapata. In these fields, an incidence rate of 100% was recorded during the sampling conducted 20 DAE. It is noteworthy that seeds from the same distributor were used, but they were different from those planted in La Mesa and Huachichil, where lower incidence rates were recorded. This information suggests the hypothesis that the seeds were infected at the time of planting, as no rapid dissemination mechanisms were observed to explain subsequent infections. In the yellow traps set up by producers, no aphids were detected, and the plants did not yet have enough foliage to allow for mechanical virus transmission. It is recommended to conduct sampling before purchasing seeds and to send these samples to a laboratory authorized by SENASICA to rule out or confirm the aforementioned hypothesis. This action could prevent producers- and consequently the region-from suffering economic losses due to reduced crop yieldThe economic losses estimated in this study differ from those reported by ^{McIntosh (2014}), who calculated that PVY has a direct economic impact of $19.56 million (approximately $326,213,027) in the state of Idaho. On the other hand, they are similar to the results of ^{Dupuis et al. (2023}), who reported yield losses of 23.5% for the most commonly cultivated varieties in Switzerland between 2004 and 2017. It is important to highlight that the incidence percentage in their study was visually assessed through symptoms caused by secondary PVY infections, a procedure not considered viable because some varieties may harbor low concentrations of the virus without exhibiting symptoms (^{Singh, 1998}). A similar situation might have occurred in this study, given that the methods used require a high viral load in the plant to detect the pathogen. However, these tools are more cost-effective considering the number of samples obtained, and they provide rapid data to assess the phytosanitary conditions of a region.

Conclusions

Yield losses caused by PVY in Fianna potato crops in the experimental plot ranged from 9.4% to 53%, while the estimated losses in the Coahuila region during the 2022 cycle were 18%, representing an economic loss of $19,068,500 for the state. These results highlight the importance of using certified PVY-free seed and protecting the crop from emergence to 60 DAE, with a particular emphasis on the first weeks. Additionally, this provides the basis for designing a more informed strategy to efficiently manage the disease and reduce the losses it causes.