APPROXIMATION TO THE ORIGIN OF FALSE MILDEW IN SAFFLOWER †

An approximation of the origin of the “false mildew” in safflower was proposed from a phylogenetic tree obtained by the Maximum Likelihood method with the genomic alignment of a nucleotide sequence of Ramularia cercosporelloides isolated from safflower lesions. The approximation is the origin of the disease known as "false mildew" in the safflower may be due to new host adaptations of Mycosphaerella graminicola.


INTRODUCTION
The "false mildew" in safflower is a disease that first emerged in the Yaqui Valley, Sonora, in the 2000-2001 agricultural cycle and has since generated problems in safflower production (Montoya 2010;JLSV, 2017).Several studies to identify the species that caused this disease (Huerta-Espino et al., 2006;Montoya-Coronado et al., 2008) coincided with the identification of the fungal genus Ramularia species that affected several crops (Videira et al., 2016).In the case of the safflower, there are discrepancies in the taxonomy show with certainty the etiological species of false mildew.
In a previous study, Ramularia cercosporelloides was found in safflower leaves collected in the Yaqui Valley (Mexico) as possibly responsible for the "false mildew" disease in safflower (Quintana-Obregón et al., 2013).However, the origin of the disease has not yet been clarified.The aim of this report is to generate an approximation of the origin of the false mildew with phylogenetic analysis, which may help to find the origin of the disease.† Submitted October 23, 2018-Accepted March 12, 2019.This work is licensed under a CC-BY 4.0 International License.

MATERIAL AND METHODS
A nucleotide sequence was obtained beforehand as of pure isolate from safflower leaves infested with false mildew by Quintana-Obregón et al. (2013) for make phylogenetic trees.The nucleotide sequence was compared to sequence related species from the National Center for Biotechnology Information (NCBI).The method of Maximum Likelihood was completed with the MEGA 5 (Molecular Evolutionary Genetics Analysis) software.
The technique of software used was the None method.The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown net to the branches (Felsenstein, 1985).The evolutionary distances were computed using the Jukes-Cantor method (Jukes and Cantor, 1969) and are in the units of the number of base substitutions per site.The analysis involved 30 nucleotide sequences.All ambiguous positions were removed for each sequenced pair.There were a total of 5994 positions in the final dataset.Evolutionary analyses were conducted in MEGA 5 (Neir and Kumar, 2000;Tamura et al., 2011).

RESULTS AND DISCUSSION
As a result, and online to the analysis of Maximum Likelihood (Figure 1), the isolate obtained in the Yaqui Valley was identified in the phylogenetic tree as Ramularia from safflower (Mexico), associated with the nucleotide sequence of Mycosphaerella graminicola CBS 100335 (asexual form=Septoria tritici) phytopathogenic of Triticum aestivum (wheat) (Ponomarenko et al., 2011).Septoria tritici is identified in wheat in the Netherlands (Crous et al., 2007;Verkley et al., 2004).
The Yaqui Valley is the major producer of wheat in Mexico.This crop represents one of the main inputs in cereal production (Berber et al., 2014).Before the year 2000, false mildew had not been reported as a problem in safflower, but because of the proximity between the areas for wheat and safflower cultivation in the Yaqui Valley, it is possible the hypothesis an adaptation in M. graminicola that could be favored by a change of reproductive cycle in this crop, severely affecting its production.Adaptation to new host plants of the asexual cycle (Ramularia) of Mycosphaerella labyrinth been associated with plant diversity as a survival mechanism (Videira et al., 2015).The change from sexual cycle (Mycosphaerella) to asexual (Ramularia) is an adaptation mechanism that could have developed in the Yaqui Valley.The ancestral specie shown in Figure 1 with Ramularia supports the hypothesis presented.Moreover, a study on cotton grown in Brazil where relationships found between sexual and asexual cycles of an isolated of Ramularia areola identified as Mycosphaerella areola, allowed researchers to visualize a survival mechanism of Ramularia (Metha et al., 2016).This approximation opens new windows of investigation that allow full identification of the false mildew.

CONCLUSION
Based on the results obtained from this approach, the pathogen that produces false mildew in safflower this related to Mycosphaerella.However, more research is needed to study the pathogen and the sexual cycle of Mycosphaerella graminicola, to provide a more precise identification, and to explain its association with false mildew.It is important to find the origin of the causative agent of the disease to design control strategies and explain defense and adaptation mechanisms for better control of the pathogen.

Figure 1 .
Figure 1.Phylogenetic tree built by the method Maximum Likelihood.