Producing regions

The field phase was carried out from March to November 2015. Three commercial orchards of avocado ‘Hass’ were selected in three producing regions with different types of climate each: The ‘El Parejo’ orchard owned by the SPR of RL PARGUT with climate warm sub-humid located at 1 151 m altitude in Tepic, Nayarit; the “Paso de Carretas” orchard of the RL Agro González SPR, in Gómez Farias, Jalisco, with subhumid subhumid climate and altitude of 2 180 m and the orchard “El Parejo” by José Manuel Báez in temperate climate at 1 579 m altitude in Uruapan, Michoacán. All orchards had a micro sprinkler irrigation system and received the standard management of each region.

Climatic characterization

The sub-humid warm climate (Aw2) has an average annual temperature higher than 22 °C and the temperature of the coldest and warmest month above 17 and 22 °C, respectively; the precipitation of the driest month varies between 0 and 60 and summer rains with a precipitation/temperature ratio (P/T index) greater than 55.3 and winter rainfall percentage of 5 to 10.2% of the annual total. In the semi-warm sub-humid climate (AC(w)) the average annual temperature is higher than 18 °C, the temperature of the coldest and hottest month is less than 18 and 22 °C, respectively; the precipitation of the driest month is less than 40 mm and summer rains with a P/T index between 43.2 and 55 and a winter rainfall rate of 5 to 10.2% per year. In the temperate climate (C(m)) the average annual temperature is between 12 and 18 °C, the temperature of the coldest month between -3 and 18 °C and the temperature of the hottest month lower than 22 °C; the precipitation in the driest month is less than 40 mm; summer rainfall and winter rainfall rate of 5 to 10.2% of the annual total (^{García-Amaro, 1973}).

Climatic information

The average climatic data and monthly cumulative precipitation were collected from the national meteorological service’s website (www.smn.cna.gob.mx), the information corresponds to the last climatology (1981- 2010) which was calculated with the daily records of each variable. In order to characterize the temperature and precipitation conditions of each region, the meteorological station closest to the orchard was used as reference (Table 1).

Fruit sampling

In each orchard was selected a group of 25 trees (five replicates made up of five trees each). In each tree 20 fruits of the “main” or “normal” flowering occurred in January-February 2015 and were located in the south-west orientation and the middle and outer part of the tree canopy. For each sampling date, five trees were randomly selected, in each of which four fruits were collected at different stages of development according to their diameter (Table 2). After being collected, the fruits were transferred to the Laboratory of Frutifisiology of the Experimental Field Santiago Ixcuintla-INIFAP where they were washed with distilled water with sodium hypochlorite (200 mg L^-1) and weighed in a precision balance (Ohaus model P2001, Florham, NJ, USA). The length and diameter were obtained with a digital vernier (MTC500-196, Mitutoyo Corp., Sakado, Japan).

Sections of fruit evaluated

For each development stage of the collected fruit three skin samples were obtained (one per section). Which were separated from the pulp with a vegetable peeler. The sections evaluated were: ventral lateral equatorial (ELV), superior dorsal front (SFD) and superior ventral frontal (SFV) (Figure 1).

Figure 1 Sections evaluated for avocado ‘Hass’ fruit. 

Measurement of roughness

A 2×2 cm (3 648×2 736 pixels) image was obtained for each of the fruit sections using a stereomicroscope (Zeiss Model Stemi 2000-C; Barrington, NJ, USA) to which he set up a digital camera (Canon model Power Shot G11; NY, USA). Each image was incorporated into the ArcView version 3.2 geographic information system and the “Spatial Analyst” module quantified the surface with a slope greater than 20%. The roughness was expressed as the rough surface (cm²) with respect to the total area of the analyzed image (rough surface/total area, cm² cm²).

Classification of roughness

The surface values were converted to a percent roughness value with respect to the total area of the analyzed image. The classification was according to its leve lof roughness, according to the scale of ^{Salazar-García et al. (2016b)} (Figure 2).

Figure 2 Scale of roughness level of avocado ‘Hass’. 

Analysis of the information

The monthly data of temperature and precipitation were organized in the program MS Excel version 2013. Later, a climogram was elaborated to graphically analyze the thermal and humidity distribution of the three study areas.

The roughness variables that were statistically analyzed were: roughness of the ventral lateral equatorial section, roughness of the dorsal frontal superior section and roughness of the ventral frontal superior section. An analysis of variance was performed where the experimental units were the three sections of the fruit, as treatments the development stages of the fruit (5) and the variation factor was the type of climate (3). A completely randomized experimental design and comparison of means were used with the Tukey test p≤ 0.05. The analysis was performed with the statistical program Minitab version 17.

Climatological description of the producing regions

The climatic parameters showed differences between the study regions. The mean annual temperature was differentiated between regions at 2 °C on average (up to 4 °C between temperate and warm sub-humid). In the subhumid warm climate, the highest average monthly temperatures were recorded (22 °C) and in the coldest temperatures (18 °C). There were also differences in the monthly temperature throughout the year and the highest records corresponded to the warm subhumid climate. The coldest summer occurred in the temperate climate; however, the colder months were in the sub-humid semi-warm climate (December and January).

The annual precipitation also varied between climates, contrasting between the highest 1 450 mm (temperate) and the lowest 710 mm in the subhumid sub-humid climate. For the three types of climate, in the summer (June to September) precipitation > 75% of the annual rainfall. The wettest months were July in warm subhumid and temperate (367 and 315 mm respectively) and august for sub-humid (151 mm). Winter rainfall (December to February) varied between 40 and 66 mm between climates, representing < 6% per year. In the temperate climate, 51% more precipitation (annual average) precipitated than in the semi-warm sub-humid climate and 14% more than in warm sub-humid.

The previous description of the three climates coincides with that published by ^{García-Amaro (1973)}, particularly with the thermal conditions and the distribution of the monthly precipitation, which confirms the adequate selection of stations that allowed to characterize the environment of the study areas. With respect to the contrasts in the climatic variables between the three types of climate, the results agree with ^{Salazar-García et al. (2016a)} and ^{Álvarez-Bravo and Salazar-García (2016a)} corroborating the climatic diversity in which ‘Hass’ occurs in the western region of Mexico (Figure 3).

Figure 3 Average temperature and cumulative precipitation of the climatology corresponding to the period 1980-2010. 

The cv. Hass was selected in La Habra Heights (^{Hass, 1935}), southern California, USA where the climate is Mediterranean type Csb (^{NOAA, 2017a}) and characterized by an average annual temperature higher than 19 °C. In this region, throughout the year the average monthly temperature has fluctuations greater than those found in the present work. The average temperature of the coldest month is less than 15 °C (lower than the temperate climate) and the warmest month above 24 °C (higher than the warm subhumid climate) (^{NOAA, 2017b}). This shows the wide range of adaptation of the avocado ‘Hass’ to the environmental conditions.

Roughness by sections of the fruit

The roughness of the skin of the avocado ‘Hass’ presented clear differences between the three sections evaluated according to the climate where the fruit was produced a nd during its development (Table 3). In the warm subhumid climate, the section with the highest roughness consistently from olive to harvest was ELV. The SFD and SFV sections in stage I (0.86 and 0.82 cm², respectively) and stage II (0.77 and 0.82 cm², respectively) had a higher roughness. From stage III until harvest there were no differences between the three sections.

In the temperate climate there were only differences in the Olive stage, where the ELV section presented greater roughness (0.65 cm²) than the other sections (Table 3). The analysis between climates showed difference for each one of the sections evaluated in the different stages of development of the fruit. The ELV section in most of the growth stages, with the exception of olive (0.83 to 0.86 cm²) and harvest (0.65 to 0.75 cm²) where it showed no differences with the subhumid semicurid, presented more rugged fruits in warm subhumid climate. On the other hand, the SFD section, which did not show stable behavior, only showed statistical differences between climates in stage II (0.74 to 0.78 cm²). Finally the SFV section was superior (0.86 cm²) in the olive stage in the semi-warm sub-humid climate. In stage I and stage II showed no differences between climates, while in harvest was higher (0.75 cm²) in warm subhumid (Table 3).

In the analysis between sections of the fruit there were always differences between climates. In the warm subhumid climate the highest roughness values were​ recorded in ELV and SFD for all stages of fruit development. In stages I, II and III the fruits of the semi-warm sub-humid climate were similar to those of the warm sub-humid climate for the SFV section. The results coincide with what ^{Álvarez-Bravo and Salazar-García (2016b)} mentioned for ‘Hass’ fruits produced in warm subhumid climate. These authors found results similar to the present study where fruits produced in subhumid warm climate orchards had high and very high roughness records, clearly differentiating from temperate and sub-humid fruits with lower roughness (low and medium, respectively) (Table 3 ).

Proportion of fruits according to their level of roughness per section

Ventral lateral equatorial. The 67% of the fruits of the warm subhumid climate were classified in the high roughness level, in contrast to the fruits of the subhumid and temperate semi- warm climate, which presented average roughness (36 and 42%, respectively). The fruits with very high roughness were only recorded in warm subhumid climates (in all stages of fruit development) and subhumid (with the exception of harvesting). In most stages of fruit development, the high roughness level was most frequently present in warm subhumid climate. Their presence varied from 75 to 80% of the fruits (except harvest). Less rugged fruits were those of the temperate climate, collected in the olive stage (40%) and harvest (50%) (Figure 4).

Figure 4 Distribution of avocado ‘Hass’ fruits according to the level of roughness in the ventral lateral equatorial section harvested in five stages of development.  

Upper dorsal front. In the warm subhumid climate, from Olive stage to harvest, the proportion of fruits that showed high roughness was 40 to 80%. Only in stage I, 30% of the fruits presented very high roughness level. In the sub-humid semi-warm climate, fruits with a medium roughness level prevailed. In the olive stage 45% of the fruits presented this condition while in the harvest reached up to 60%. In stage III, 35% of the fruits showed low roughness level. As in the sub-humid semi-warm climate, in the tempering, fruits with a medium roughness prevailed. The highest proportion was recorded in stage III (55%). On the other hand, 75% of the fruits in the olive stage showed low roughness level (Figure 5).

Figure 5 Fruit distribution according to the level of roughness in the upper front dorsal section. 

Superior frontal ventral. Only fruits from the semi-warm subhumid climate showed very high roughness (particularly in the olive, I and III stages). In warm subhumid and subhumid climates, high-grade roughness predominated with 63 and 49% respectively, while in the temperate climate the average roughness (44%) prevailed. The most marked difference between fruits of the three types of climate was observed in the low level of roughness to harvest (5, 25 and 55% in warm subhumid, subhumid and warm temperate, respectively) (Figure 6).

Figure 6 Fruit distribution according to the level of roughness in the ventral frontal superior section. 

Evolution of roughness level

The roughness of the fruits produced in the warm subhumid climate, evolved from olive to harvest. On average, they had a high roughness level. In the subhumid semi-warm climate, the roughness of the fruits decreased from the high level in olive size, to the average harvest level. On the other hand, the fruits of the temperate climate fluctuated from the average level of roughness in olive size to high level in stage I, until it diminished to the low level in harvest. With similar results, ^{Álvarez-Bravo and Salazar-García (2016b)} concluded that the roughness tends to decrease from Stage I to harvest in fruits produced in warm subhumid climate (Figure 7).

Figure 7 Evolution of the average roughness level of the three sections according to climate.