IMPROVE YIELD AND DOWNY MILDEW RESISTANCE OF F1 MADURA MAIZE HYBRIDS

Maize production in Madura Island is low. The study aimed to evaluate the agronomic performances (flowering age, harvesting age, and yield), heterosis effect, and resistance to downy mildew disease of F1 Madura maize hybrids. Ten F1 maize hybrids and seven respective parents were evaluated at the experimental center of the Agro-Technology Study Program of Agriculture Faculty, the University of Trunojoyo Madura, from July to December 2017. The experiments were arranged in a randomized block design, three replications, with a 50–100 plant population per unit. The parents were T12, T16, G10, G14, E02, Td04 and L1 genotypes having resistance to downy mildew (Peronosclerospora maydis). The results showed that the flowering age of the F1 Madura maize hybrids ranged 35–39 days, the harvesting age was 74–81 days, and the yield ranged from 2.90–6.40 t ha-1. Three hybrids showed the highest yield (T12 x L1 = 6.40 t ha -1, T16 x L1 = 5.42 t ha -1, and E02 x L1 = 5.90 t ha-1), and resistance to downy mildew, i.e. T12 x L1 (26.67%), T16 x L1 (26.67%), and E02 x L1 (26.67%). Two hybrids showed the highest heterosis values for yield, i.e. T12 x L1 (65.80%) and E02 x L1 (54.65%). The study suggests that three F1 Madura maize hybrids (T12 x L1, T16 x L1 and E02 x L1) are prospective to be developed further for high yield and resistance to downy mildew. [


INTRODUCTION
Maize is one of important crops widely cultivated by farmers in Madura, East Java, Indonesia. The maize planting area in Madura is around 360,000 hectares (Amzeri 2018). But, maize yield in Madura is the lowest compared to other maize production centers in East Java. Maize yield at the farm level in Madura in 2016 was only 2 t ha -1 , while maize yield in East Java achieved 5.08 t ha -1 (Pusat Data dan Informasi Pertanian 2016; Amzeri 2018).
The causes of the low yield of maize in Madura are: (1) less fertile land, (2) low rainfall, and (3) use of nonsuperior seeds (Amzeri 2009). The ways to solve these problems could be through (1) improving the environmental conditions in which the plant grows and develops, and (2) assembling a variety that is resistant to biotic or biotic environmental stresses and has a high yield potential through breeding programs. The second method is more popular than the first one.
The improved appearance of plants can be through the utilization of heterosis effect. The heterosis phenomenon is the action and interaction of good dominant genes collected in one F 1 genotype as a result of crossing two parents (Amzeri 2015). The use of heterosis in some food crops through the formation of hybrid varieties shows favorable results in cross-pollinating plants (Bairagi et al. 2002;Patel et al. 2010). Heterosis is widely used to improve the adaptability of hybrid varieties. According to Patel et al. (2010), maize yield increased after breeders assembled more hybrid varieties compared to composite ones.
Downy mildew is a major disease in maize that is caused by Peronosclerospora maydis. The disease has caused a huge loss to maize farmers. According to Soenartiningsih (2015), Yasin and Zubachtiroddin (2006), yield loss due to downy mildew can reach 100%. One step to control the disease is by using resistant varieties, because it is more stable, economical, and does not cause effects such as poisoning and environmental pollution. Based on the description above, identification of heterosis and disease resistance in maize genotype is needed as a basis for assembling hybrid maize varieties suitable for Madura environtmental conditions. The purpose of this study was to evaluate the agronomic performances (flowering age, harvesting age, and yield), heterosis effect, and resistance to downy mildew disease of F 1 Madura maize hybrids.

Plant Materials
The study was conducted at the experimental center of the Agro-Technology Study Program of Agriculture Faculty, the University of Trunojoyo Madura, from July to December 2017. The study used ten combinations of Madura maize crossing, i.e. T 12 x L 1 , T 16 x L 1 , G 10 x L 1 , G 14 x L 1 , E 02 x L 1 , Td 04 x L 1 , T 12 x G 10 , G 10 x E 02 , G 10 x Td 04 , Td 04 x E 02 , and 7 parents i.e. T 12 , T 16 , G 10 , G 14 , E 02 , Td 04 and L 1 , so there were 17 genotypes. The characters of the seven parents were shown in Table 1.

Experimental Design to Measure the Heterosis Value
The study was arranged in a randomized complete block design, ten combinations of Madura maize crossings and seven respective parents, three replications, so there were 51 experimental units. Each experimental unit was a 10 m x 2 m size, and planting distance was 20 cm x 70 cm. Therefore, the plant population in each unit was 100 plants. Observations were made on 40 randomly selected plant samples from each experimental unit. The observed characters were flowering age, harvesting age, and yield. The yield of 40 samples was then converted to a plant population of one hectare.

Resistance Assay to Downy Mildew
The experiment was arranged in a randomized complete block design, which consisted of 10 genotypes (10 combinations of the crossing), and three replications, so there were 30 experimental units. The size of the experimental unit was the same as described above, but only 20 plant samples were observed from each unit. Three weeks before the maize hybrids planted, the downy mildew susceptible maize variety (G 14 ) was planted in three rows at the edge of and among each block as the spreader plants for the downy mildew diseased source plants. When these spreader plants grew, the plants were inoculated by spraying with the spores of downy mildew following the method of Azrai et al. 2000). When the spreader plants were infected with downy mildew > 50%, then ten hybrid genotypes of maize were planted in the experimental units.

Data Analysis
Heterosis estimation values were assessed as the middle value of the square of the two parents (mid-parent) by using the formula of Hallauer et al. (2010) and Weber et al. (1970) (2019) The downy mildew resistance category was calculated following Talanca (2009) as presented in Table 2.

Agronomic Characters
The F 1 Madura maize plants started to flower at 35-39 days, and the harvesting time was at 74-81 days after planting. The maize yield ranged from 2.90 to 6.40 t ha -1 (Table 3). These results indicated that the parent combination significantly affected all the three main agronomic characters observed, i.e. the flowering age, harvesting age, and yield. The shortest flowering age was shown from the T 12 x G 10 , G 10 x E 02 , G 10 x E 02 , and G 10 x Td 04 crossings. The Td 04 x E 04 crossing showed the shortest harvesting age, whereas the longest was T 12 x L 1 crossing.

Heterosis Value
Heterosis values for the flowering age of the F 1 Madura maize hybrids greatly varied from -3.90 to 4.48 (Table  Td 04 x E 02 35 a 74 a 3.01 a The numbers followed by the same letter in the same column were not significantly different based on Duncan's test at α = 5%.  ). The existence of the positive heterosis value in this study is desirable. The magnitude of the heterosis value in several parent combinations was due to the genetic relationship of parents that relatively far away compared to other parent combinations (Barth et al. 2003;Birchler et al. 2010;Ruswandi et al. 2005).
For the flowering age, the heterosis values of the two hybrids showed negative (Table 4), while for the harvesting age, five hybrids were also negative (Table 5). Madura maize hybrids that had the best heterosis value for the harvesting age were those that had a negative value because they had a faster harvesting age than the average of both parents (Bairagi et al. 2002). Five hybrids, i.e. T 12 x L 1 , T 16 x L 1 , G 14 x L 1 , E 04 x L 1 , and Td 04 x L 1 showed early maturity ( Table 5).
The heterosis value of yield of the F 1 Madura maize hybrids showed that several cross combinations had heterosis values varying from -7.53 to 65.80% (Table 6). The highest heterosis value (65.80%) was obtained by hybrid resulting from the crossing of T 12 x L 1 followed by E 02 x L 1 (54.65%). This value indicated that the two hybrids had a higher yield than the parents. Therefore, both hybrids can be used to assemble varieties that have a high yield.
Heterosis values of the F 1 Madura maize hybrids were influenced by genetic diversity and genetic distance of parents used. High heterosis values exceeding the average of its parents indicated broad genetic diversity among individuals in the population (Poehlman 2013;Tulu 2004). The crossing of two parents with a far genetic distance will produce high heterosis, meaning that high heterosis was produced by a crossing between two parents who had many different characters. According to Mangoendidjojo (2007), heterosis was caused by the interaction of several genes, especially dominant genes.

Resistance to Downy Mildew
The downy mildew resistance of the F 1 Madura maize hybrids varied (Table 7 and 8). The downy mildew disease symptoms were first seen at seven days after planting. However, after the plant became older, i.e., days, the disease did not appear probably in stationary phase (Korlina and Amir 2015;Kim et al. 2017). The experiment showed that ten F 1 Madura maize hybrids had a disease occurrence at 42 days after planting ranging from 26.67% to 93.33% (susceptible to very susceptible category).
Based on the data of disease infection rate, the infection rate declined with increasing age of plants probably because the plant tissue becomes older and harder. In older plant tissues, the downy mildew occurs as local symptoms. As a result, the older age of the plants will be more resistant to disease. According to Agrios (2005), the younger the plant was infected, the more quickly the disease develops. The study showed that G 10 x Td 04 crossing had the highest disease attack   (Table  9).
Various factors attributed to the high disease intensity are (1) poor resistance of the plant to downy mildew, (2) highly virulent pathogen infecting the plant, and (3) environmental conditions at the time of research. According to Soenartiningsih (2015), in resistant plants, pathogen development will be inhibited, and the virulence level will decrease, whereas, in susceptible plants, the process of pathogen development goes well.
In observing the disease severity at 14 to 42 days after planting, three hybrids had the lowest attacking level. The three hybrids were resulted from crossing of T 12 x L 1 , T 16 x L 1 , and E 02 x L 1 . At 42 days after planting, the three hybrids had an attacking intensity by 26.67% (moderately resistant category). According to Hakim and Dahlan (1974) and Pajrin et al. (2013), low disease severity was thought to be because the hybrid had the resistance trait which was regulated by many genes (quantitative character) from one gene chromosome, so that even though climate factors and virulent pathogens support the occurrence of infection, these hybrids still survive from the attack of downy mildew. Furthermore, Aday (1975) and Singburaudom and Renfro (1982) stated that major genes controlled downy mildew resistance so that it was a qualitative trait.
In plant breeding programs, the purpose of crossing among parents is to get hybrids that have superior characters. The characters expected in this research were short harvesting age (early maturity), high yield, and resistance to downy mildew. The study implies that three Madura maize hybrids, i.e. T 12 x L 1 , T 16 x L 1 , and E 02 x L 1 need to be developed further for superior varieties.

CONCLUSION
Ten F 1 Madura maize hybrids have evaluated for flowering age, harvesting age, and yield, as well as downy mildew resistance. The flowering age ranged 35-39 days, the harvesting age was 74-81 days, and the yield ranged 2.90-6.40 t ha -1 . Three crosses showed highest yield (T 12 x L 1 = 6.40 t ha -1 , T 16 x L 1 = 5.42 t ha -1 , and E 02 x L 1 = 5.90 t ha -1 ) compared with their parents and resistance to downy mildew (T 12 x L 1 = 26.67%, T 16 x L 1 = 26.67%, and E 02 x L 1 = 26.67%). The highest heterosis values for yield was shown by two crosses, i.e. T 12 x L 1 (65.80%) and E 02 x L 1 (54.65%). The study suggests that the three F 1 Madura maize hybrids (T 12 x L 1 , T 16 x L 1, and E 02 x L 1 ) can be evaluated further for high yield and resistance to downy mildew.