Neotrop Entomol DOI 10.1007/s13744-016-0458-y

PEST MANAGEMENT

Influence of Different Rice Cultivars on Schizotetranychus oryzae Development D GONÇALVES1 , US DA CUNHA2, TFS RADAELLI1, NJ FERLA1 1

Laboratório de Acarologia, Museu de Ciências Naturais, UNIVATES Centro Universitário, Lajeado, Rio Grande do Sul, Brasil Programa de Pós-Graduação em Fitossanidade, Faculdade de Agronomia “Eliseu Maciel” FAEM-UFPel, Capão do Leão, Rio Grande do Sul, Brasil

2

Keywords Oryza sativa, IRGA 424, BRS sinuelo CL, BRS 7 taim, life table Correspondence D Gonçalves, Laboratório de Acarologia, Museu de Ciências Naturais, UNIVATES Centro Universitário, Avenida Avelino Tallini, 171, 95900-000 Lajeado, Rio Grande do Sul, Brasil; [email protected] Edited by André L Lourenção – IAC Received 21 December 2015 and accepted 13 October 2016 * Sociedade Entomológica do Brasil 2016

Abstract Schizotetranychus oryzae Rossi de Simons (Acari: Tetranychidae) is considered one of the most important phytophagous mite in rice cultivation in the Americas South, Central, and North. This study aimed to examine some biological aspects of S. oryzae developing on leaves of three different cultivars of rice [Oryza sativa (L.)—Poaceae] produced in the state of Rio Grande do Sul, Brasil. The plants were kept in a room at 25 ± 1°C, with natural light (photophase of approximately 14 h) and 70 ± 5% relative humidity. During the immature stages, observations were carried out daily at 7 am, 1 pm, and 7 pm. The results showed that the mean duration of the egg–adult period in days were similar between cultivars evaluated (Irga 424, 11.27 ± 0.13; Taim, 11.21 ± 0.14 and Sinuelo, 11.13 ± 0.15). Egg–adult viability on Irga 424, Sinuelo, and Taim was 61.9, 85.71, and 90.48%, respectively, being lowest on Irga 424 (χ2 = 28.62, p < 0.0001). The duration of the immature stages was not affected by cultivar, but on Irga 424, egg– adult viability and female longevity were lower. The results of this study can help select O. sativa cultivar resistant to S. oryzae. However, historically, the IRGA 424 has lower populations of S. oryzae in field conditions.

Introduction The genus Oryza (Poaceae) includes 20 wild species and two domesticated species, namely Asian rice (Oryza sativa L.) and African rice (O. glaberrima L.). Rice is the third most cultivated cereal in the world and occupies an area of 158 million hectares accounting for 20% of calories consumed as food worldwide (USDA 2015). Recently, Brasil became the ninth leading rice grower in the world, with production of 12.3 million tons, and the state of Rio Grande do Sul accounts for approximately 69% of this domestic production (IBJE 2015). Due to demand for increased production, new management technologies are constantly introduced especially new cultivars. However, despite the increased yield potential of the crop, largely due to the genetic improvement of new cultivars, issues such as with plant health can significantly reduce production if adequate

management measures are not adopted. Also noteworthy is the emergence of insects and mites unknown so far as to economic importance. Among the mites, Schizotetranychus oryzae Rossi de Simons (Tetranychidae) has emerged as the most important phytophagous mite in commercial crops of Rio Grande do Sul State (Ferla et al 2013). In Brasil, S. oryzae had been already registered in the states of Rio de Janeiro, Espírito Santo (Barcellos et al 1979), and São Paulo (Rossetto et al 1971). Flechtmann (1985) recorded the occurrence of this species in Corrientes, Argentina and in the state of Rio Grande do Sul, Brasil, and since then, it has become known as a pest potential for rice. The plants infested by S. oryzae present creamy white areas visible along the ribs on the adaxial side of the leaves. These symptoms appear more intense by the presence of these mites producing webs to form their colonies and can be mistaken for viruses (Barcellos et al 1979).

Gonçalves et al Table 1 Mean duration in days (±SE) of the immature stages of Schizotetranychus oryzae on three different rice cultivars under laboratory conditions. Photophase of 14 h at 25 ± 1°C and 70 ± 5% RH. Stages

Sinuelo N*

Irga 424 Duration (days) 4.9 ± 0.07a**

Viability (%)

N

Taim

Duration (days)

Viability (%)

N

Duration (days)

Viability (%)

Egg

21

100

19

4.91 ± 0.06a

90.48

21

4.89 ± 0.06a

100

Larva

20

1.05 ± 0.04a

95.24

19

1.06 ± 0.06a

100

21

0.98 ± 0.05a

100

Protochrysalis Protonymph

19 19

1.05 ± 0.06a 0.8 ± 0.03a

95 100

15 15

1.1 ± 0.17a 0.79 ± 0.06a

78.95 100

20 20

1.14 ± 0.05a 0.88 ± 0.06a

95.24 100

Deutochrysalis Deutonymph

19 19

0.98 ± 0.06a 1.22 ± 0.08a

100 100

13 13

1.03 ± 0.05a 1.13 ± 0.08a

86.67 100

20 19

0.89 ± 0.03a 1.18 ± 0.08a

100 95

Teleiochrysalis

18

1.28 ± 0.04a

94.74

13

1.21 ± 0.05a

Egg–adult

18

11.13 ± 0.15a

85.71 A***

13

11.27 ± 0.13a

100

19

1.3 ± 0.03a

61.9 B

19

11.21 ± 0.14a

100 90.48 A

*Number of mites evaluated. **Means followed by lowercase letters in a row differ significantly by the Tukey test (p < 0.05). ***Means followed by different uppercase letters in a row differ significantly by the χ2 test (p < 0.05).

Possible damage caused by S. oryzae in rice grown, as well as some biological aspects, and the influence of different cultivars on the populations of this mite are unknown, which hampers the establishment of an appropriate management program in rice. Accordingly, the present study aimed to determine some biological aspects of S. oryzae developing on three O. sativa cultivars recommended for cultivation irrigated in Rio Grande do Sul.

Material and Methods The experiments were carried out in the Acarology Laboratory of UNIVATES University Center using three Oryza sativa cultivars recommended for cultivation irrigated in Rio Grande do Sul: IRGA 424 (Irga 424), BRS Sinuelo CL (Sinuelo), and Embrapa BR7 Taim (Taim). Stock colonies of Schizotetranychus oryzae—the stock colonies of S. oryzae—were established from samples collected in rice fields with cultivar (Inta Puita CL) in Capão do Leão County, Rio Grande do Sul State (31°48′ 43.18"S and 52°27′56.06"W). Specimens of S. oryzae Table 2 Mean fertility (±SE) and duration of periods of preoviposition, oviposition, and post-oviposition and longevity of Schizotetranychus oryzae on the different rice cultivars. Photophase of 14 h, temperature of 25 ± 1°C and 70 ± 5% RH.

were released on rice plants of the same cultivar (Inta Puita CL) and kept in 10-l pots with eight plants each, totaling 32 plants/cultivar evaluated. The plants free of infestations were kept isolated in a greenhouse for 30 days before starting the tests. An arena of 5 cm in diameter was created, enclosing it with Biostop® glue. Each plant had three arenas, totaling 21 arenas for each evaluated cultivar. The plants were planted in pots and kept in a room at 25 ± 1°C, with natural light (photophase of approximately 14 h) and 70 ± 5% relative humidity. After preparing the arenas, they were placed by a window to get natural sunlight. A female of S. oryzae was then placed in each arena, and the observations were carried out using a stereomicroscope. After laying eggs, the female was removed, leaving only one egg/arena. The study started with a total of 21 eggs/cultivars evaluated. In the immature stages, the observations were done at 7 am, 1 pm, and 7 pm, when development and viability of the specimens were evaluated. In adulthood, the evaluation was done once a day at 5 pm, when oviposition and survival were evaluated. The sex ratio was calculated using the data of individuals of parental generation.

Fecundity

N*

Irga 424

N

Taim

N

Sinuelo

Pre-oviposition Oviposition Post-oviposition Female longevity

10 10 10 10

34.7 ± 2.34a** 1.8 ± 0.13a 33.8 ± 2.04a 3.9 ± 1.17a

14 14 14 14

35.85 ± 2.72a 1.71 ± 0.24a 34.35 ± 2.57a 4.57 ± 1.09a

17 17 17 16

29.7 ± 3.5a 2.23 ± 0.43a 29.7 ± 3.59a 2.68 ± 0.45a

Male longevity Fecundity

10 1

36.09 ± 3.99a 11

15 4

37.4 ± 3.04a 17.75 ± 4.57

17 0

43.16 ± 4.64a –

*N = number of evaluated mites **Means followed by different letters in the line differ significantly by Tukey test (p < 0.05).

Life cycle of Schizotetranychus oryzae Table 3 Mean duration of each generation (T), net reproductive rate (Ro), intrinsic rate of natural increase (rm), and finite rate of increase (λ) of Schizotetranychus oryzae on different rice cultivars. Photophase of 14 h at 25 ± 1°C and 70 ± 5% RH.

Treatment

T (days)

Taim Irga 424 Sinuelo *

λ

Ro (♀/♀)

rm (♀/♀*day)

22.64 ± 0.59 a*

26.17 ± 2.23 a

0.144 ± 0.004 ab

1.155 ± 0.004 ab

21.92 ± 0.47 ab 19.99 ± 1.04 b

20.85 ± 1.30 a 25.04 ± 3.02 a

0.136 ± 0.001 b 0.160 ± 0.007 a

1.148 ± 0.002 b 1.174 ± 0.008 a

Values represent the mean ± SE obtained from jackknife method using the SAS program.

For each parameter evaluated, values followed by the same letter in the column do not differ statistically from each other (p > 0.05).

The collected data were compared using the Tukey test, except for the viability data, where the χ2 test was used, and the significance level was 5% for statistical analysis using the BioEstat 5.0 software. A fertility life table was calculated by estimating the mean interval between generations (T), net reproductive rate (Ro), intrinsic rate of increase (rm), and finite rate of increase (λ). Parameters of fertility life table were estimated by the jackknife method, using “Lifetable.sas” (Maia et al 2000), and the means compared by a two-tailed t test (p ≤ 0.05) by the SAS™ software (SAS Institute 2000). Differences between treatments were determined at the α = 0.05 level of significance (SAS Institute 2000).

424, Sinuelo, and Taim was 61.9, 85.71, and 90.48%, respectively, with the lowest being on Irga 424 (χ2 = 28.62, p < 0.0001). Mean fecundity was 34.7 ± 2.34 eggs/female on Irga 424, 35.85 ± 2.72 on Taim, and 29.7 ± 3.5 on Sinuelo (Table 2). The duration in days of pre-oviposition, oviposition, and post-oviposition periods was, respectively, 1.8 ± 0.13, 33.8 ± 2.04, and 3.9 ± 1.17 on Irga 424, 1.71 ± 0.24, 34.35 ± 2.57, and 4.57 ± 1.09 on Taim, and 2.23 ± 0.43, 29.7 ± 3.59, and 2.68 ± 0.45 on Sinuelo. Female longevity in days was 36.09 ± 3.99 on Irga 424, 37.4 ± 3.04 on Taim, and 43.16 ± 4.64 on Sinuelo. Male longevity was greater on Taim and less on Irga 424, and males were not found on Sinuelo. Mean generation time (T, days) was higher on Taim (22.64 ± 0.59) than on Sinuelo (19.99 ± 1.0) (Table 3). Net reproductive rate (Ro) was similar for the three cultivars, and the ability to increase (rm) and the finite rate of increase (λ) were higher on Sinuelo and lower on Irga 424. Higher survival (lx) of S. oryzae was between days 15 and 16 on Sinuelo, between days 14 and 31 on Irga 424, and between days 14 and 33 on Taim (Fig. 1). Specific fertility was highest between days 14 and 15 for all cultivars (Fig. 2).

Results The duration in days of the egg, larva, protocrysalis, protonymph, deutocrysalis, deutonymph, and teleocrysalis periods of S. oryzae were similar between cultivars evaluated (Table 1). The mean duration of egg–adult period, in days, was similar in all cultivars (Irga 424, 11.27 ± 0.13; Taim, 11.21 ± 0.14; and Sinuelo, 11.13 ± 0.15). Egg–adult viability on Irga 1.2

Sinuelo Irga 424

1

Taim

Survival (lx)

0.8

0.6

0.4

0.2

0 0

5

10

15

20

25

30

35

40

45

50

55

60

Days

Fig. 1 Survival (1x) of Schizotetranychus oryzae on the rice cultivars Irga 424, Taim, and Sinuelo. Photophase of 14 h, temperature of 25 ± 1°C, and 70 ± 5% RH.

Gonçalves et al 2.5 Sinuelo Irga 424 Taim

Specific ferlity (mx)

2

1.5

1

0.5

0

0

5

10

15

20

25

30 Days

35

40

45

50

55

60

Fig. 2 Specific fertility (mx) of Schizotetranychus oryzae on the rice cultivars Irga 424, Taim, and Sinuelo. Photophase of 14 h, temperature 25 ± 1°C and 70 ± 5% RH.

Discussion The present study showed that the development of S oryzae was different between cultivars only for the viability, being lower in IRGA 424. This could have been due to a different genetic trait because Sinuelo was developed by backcrossing the commercial cultivar Taim, and they showed about 88% similarity according to molecular evaluations (Sosbai 2014). These genetic differences between cultivars might have been manifested by morphological characteristics of the leaf surface, because unlike Sinuelo and Taim, Irga 424 has hairy leaves, which could hinder the establishment and development of S. oryzae. According to Alonço (2005), some unknown physiological characteristics are capable of causing antibiosis. This would explain the higher mortality rate on Irga 424. However, studies are needed to confirm this hypothesis. The development time of the immature stages was shorter when compared with that obtained by Mejia et al (1998) with the cultivars Bluebonnet 50 (BBT 50) and Cica 8 (15.9 and 16 days, respectively), where this difference may be associated with the methods used during the experiments, the climate, and especially the rice cultivars. According to Magalhães et al (2007), mites adapt to their hosts and local environmental conditions. That would explain the difference between populations of S. oryzae in this study and those used in the studies by Mejia et al (1998). The population growth parameters determined in Sinuelo and Taim cultivars are similar to those obtained for Tetranychus desertorum Banks, Tetranychus neocaledonicus André, and Tetranychus pacificus McGregor (Tetranychudae), species considered pests with high biotic potential (Sabelis 1985). Accordingly, the results obtained in this study indicated that possible

economic losses caused by the attack of S. oryzae may be higher when using the Sinuelo and Taim cultivars in rice fields in Brasil. Sinuelo and Taim seemed to be more susceptible to S. oryzae, while Irga 424 showed higher mortality, indicating that it was less favorable for the development of S. oryzae under laboratory conditions. However, further studies are necessary under field conditions to test this hypothesis. However, Ferla et al (2013) found high populations on Irga 424 crops in the city of Taquari, Rio Grande do Sul. These differences are possibly related to adverse environmental factors found in field conditions. These results contribute to our understanding of the biological aspects and development of S. oryzae on the different rice cultivars. Given the importance of this mite in rice production, this study makes important contributions to the establishment of integrated management programs of this important mite.

Conclusions No significant differences were observed in S. oryzae development time between cultivars. The cultivar Irga 424 showed lower viability in the egg–adult period, thus, being less favorable to S. oryzae development under laboratory conditions when compared with Sinuelo and Taim. Acknowledgments We are thankful to CNPq and UFPel for granting the doctoral scholarship, to Univates University Center for providing the facilities of the Acarology Laboratory to carry out the work, and to Professor Dr. Carlos Holger Wenzel Flechtmann for his cooperation in getting referrals. We are also grateful to the anonymous reviewers and associate editors for their contributions in improving the article. Dr. A. Leyva helped with the English editing of the manuscript.

Life cycle of Schizotetranychus oryzae

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