Introduction

Until the mid-eighties of the twentieth century, due to the production of rice (Oriza sativa L.) thin long grain ‘Sinaloa type’, in Mexico there was self-sufficiency in this cereal (^{Hernández, 2016}). With the incorporation of the country to the General Agreement on Tariffs and Trade (GATT) in 1986, import permits for agricultural products were transformed into tariffs and in 1989, the guarantee price for basic grains, including rice, was eliminated. (^{Calva et al., 1998}). In 1994, the North American Free Trade Agreement (NAFTA) entered into force and tariffs on rice imports were eliminated mainly from the United States (^{Bartra, 2005}).

With the commercial opening in 2000, the ‘Sinaloa type’ rice lost competitiveness due to the massive importation of rice of the same type of grain, favored by the production and commercialization at low prices, generated by the high subsidies received by producers in the United States of America (^{Ireta et al., 2011}). The consequences were reflected in a drastic reduction in the area planted and in the production volumes of thin long grain rice in the country (^{Chávez-Murillo et al., 2011}).

Currently 75% of the rice consumed in Mexico is imported and with long thin grain, in 2015, 1 062 500 tons were imported at a cost of three hundred million dollars, equivalent to six billion pesos annually (^{Hernández, 2016}). Only 25% of the consumption is supplied by the national production, of which the fourth part is ‘Morelos rice’ (long with 20% of ‘white belly’) and three quarters is Filipino Milagro rice (medium with 10% of ‘white belly’) (^{SIAP-SAGARPA, 2016}).

To help solve this situation, INIFAP, with the financial support of the Sector Fund SAGARPA-CONACYT in synergy with the Latin American Rice Irrigation Fund (FLAR) of the International Center for Tropical Agriculture (CIAT) of Cali, Colombia, during the 2012-2015 period carried out selection activities (^{Álvarez et al., 2016}; ^{Barrios et al., 2016a}) and biometric evaluation of thin long grain rice materials (^{Barrios et al., 2016b}) under the environmental conditions of the tropics dry and wet of Mexico. In view of this situation, the proposed objectives were to generate new multi-environmental varieties of long-grain rice with a high and stable yield, resistant to diseases prevalent in Mexico, with good industrial grain quality, and competitive with imported rice; and produce and deliver high quality seed for the establishment of certified seed production programs, which contribute to the recovery of production levels of thin long grain rice in Mexico.

Materials and methods

During the year 2012, nurseries identified as VIOFLAR-2008, VIOFLAR-2009, VIOFLAR-2010 and VIOFLAR-2011 were introduced from FLAR, and integrated by 40, 35, 40 and 226 F₅ lines, respectively.

The pre-selected materials were established and evaluated through preliminary yield tests (PPR), preliminary yield trials (EPR), compact yield trials (ECR) and technology validation in contrasting ecosystems and moisture regimes of different localities of the dry tropic of the Pacific slope and of the Depression of the Balsas, as well as of the humid tropic of the Gulf of Mexico (Table 1) in turn, the evaluation of the industrial quality of the grain was made in the laboratory of the Experimental Field Zacatepec of the INIFAP, located in Zacatepec, Morelos.

Results

In Table 2, the average grain yields of the ECR 2015 established in the rice localities of Mexico are presented. As can be seen, there is variation in the behavior of the materials between localities, some with higher yields such as Paracuaro, Michoacán and Santiago Ixcuintla Nayarit, followed by the other evaluated localities, with the exception of the locality Huimanguillo, Tabasco (temporary), which was the one that obtained the lower yields (Table 2).

As can be seen in Table 3, the environments in which the 15 genotypes reported yields of more than 10 t ha^-1 were: Paracuaro, Michoacán, Sauta, Nayarit and Zacatepec, Morelos; the three sites are located in the dry tropics and the cultivation takes place under irrigation conditions; in Ebano, San Luis Potosí, located in the sub-humid tropics, also with conventional irrigation was slightly below 10 t ha^-1. In Buenavista, Colima, where the crop grows in rainy conditions with precarious irrigations, the yield was lower than reported, just like El Gargantillo, Jalisco located in the dry tropics, with irrigation regime and thin lateritic soils. On the other hand, for the Town C-21 of Huimanguillo, Tabasco, located in the humid tropics and common temporary moisture regime, the yield was the lowest of all (Table 3).

In the Table 4 shows the results of the average yields of the 15 genotypes through the ‘genotype x environment’ interaction. As can be observed, the yields close to 10 t ha^-1 corresponded to the lines FL010129-12P-4-2P-3P-M, FL010164-7P-3-1P-1P-M, FL08224-3P-2-1P-3P-M and FL07562-7P-3-3P-2P-M, these last two of extra-long grain. Although the INIFLAR and INIFLAR RT varieties of medium grains (released by INIFAP in 2015), were located at the same level of significance, but their yields were slightly lower, while the yield of the Aztecas variety was the lowest expressed of all the genotypes evaluated (Table 4).

On the other hand, the stability levels of the 15 genotypes evaluated in the seven sites are presented in Table 5. It is noteworthy that the lines FL08224-3P-2-1P-3P-M and FL07562-7P-3-3P-2P-M presented a capacity to adapt in all the evaluated environments, since they were reported with acceptable stability levels with average yields of 10.1 and 9.530 t ha^-1, respectively. Some other lines, although with good yields, were also stable but not in all environments. INIFLAR R, INIFLAR RT and Silverio, are also stable in all environments, although with lower performance. The Aztecas variety and the line FL06747-4P-10-5P-3P-M have yields higher than 9 t ha^-1, but they are only stable in favorable environments (Table 5).

Discussion

The productivity of the Pacífico FL15 and Golfo FL16 varieties was 65.7 and 67.8 kg of grain per day (^{INIFAP, 2016b}). With the variety Pacífico FL15, an average yield of 9.2 t ha^-1 is obtained, which represents increases of 2.6 and 3.7 t ha^-1 of paddy rice with respect to the Aztecas commercial varieties (6.6 t ha^-1) and Filipino Miracle (5.5 t ha^-1) of the ECR. On the other hand, with the Golfo FL16 variety, an average yield of 9.5 t ha^-1 is obtained which represents increments of 2.9 and 4 t ha^-1 of paddy rice with respect to the commercial Aztecas and Filipino Miracle varieties of the ECR. In addition, with the varieties Pacífico FL 15 and Golfo FL 16, the recovery of whole polished grains increases between 9 and 33% in relation to commercial varieties (^{García et al., 2011}).

Another advantage of these varieties is that they have a high spectrum of resistance to the sogata- VHB complex (white leaf virus) and the endemic ‘rice burning’ disease (Pyricularia oryzae), as well as moderate resistance to the new disease ‘spotted grain’, caused by Helminthosporium oryzae in association with other pathogens, and stem borers (Chilo loftini, Rupela albinella and Diatraea saccharialis) (^{Hernández et al., 2013}; ^{Tapia et al, 2013}). In addition, both varieties are distinguished by their extra-long grain with excellent milling quality and good culinary quality, so they can compete with the types of grain that are being imported from Thailand and Vietnam (^{Tolentino, 2014}).

The multi-environmental varieties are of high potential yield, stable in the ecosystems of both coasts, resistant to lodging, shelling and diseases that attack this crop nationwide, with long thin grain of good industrial quality, are competitive with rice of import of this same type of grain. In addition, they will contribute to the expansion of the area and increase the production of rice with this type of grain, being a reference to counteract the import volumes of thin long grain rice, restoring the sources of work in the field and in the industry rice.

Conclusions

They were selected, purified, biometrically evaluated and released Pacífico FL 15 and Golfo FL 16, two varieties of thin long grain rice with high and stable yield potential, resistant to ‘rice burning’ and the sogata-(VHB) complex, with moderate resistance to the new disease ‘spotted grain’, to borers of the stems, and with good industrial grain quality. The multi-environmental variety Pacífico FL 15 is stable in all environments of the humid tropics of the Gulf of Mexico and the dry tropics of the Pacific Ocean. It can be grown under irrigation in both slopes, but it has greater potential in the Pacific slope. The Golfo FL 16 variety is also multi-environmental and stable in all environments of the humid tropics of the Gulf of Mexico and the dry tropics of the Pacific slope. It can be cultivated in both slopes, but it has greater potential in the plains of the Gulf of Mexico.