Severidad de huanglongbing (hlb) en genotipos de naranja [Citrus ×sinensis (L.) Osbeck], mandarina (Citrus reticulata Blanco) y limón [Citrus ×latifolia (yu.) Tanaka] en huertos

Abstract

The citrus disease known as Huanglongbing (HLB) was reported for the first time in Puerto Rico in 2009. Since then, it has spread throughout the island causing a decrease in production and reduction in the cultivated area, which does not exceed 1297 hectares. This disease is associated with the bacterium ‘Candidatus Liberibacter asiaticus’ that is transmitted by the psyllid Diaphorina citri Kuwayama. Several studies have informed that Citrus genotypes have variable levels of response to the disease. Similarly, other researches show rootstocks influence on the grafted genotypes reaction to HLB. In this context, the objective of this study was to assess visually the HLB severity in eight genotypes of mandarin (Citrus reticulata Blanco) grafted onto the rootstocks ‘C-35 Citrange’, ‘Cleopatra’ mandarin and ‘US-942’ under field conditions and the Area Under Disease Progress Curve (AUDPC) was calculated. Additionally, HLB severity in 13 sweet orange genotypes [Citrus ×sinensis (L). Osbeck] of the Citrus collection at the Adjuntas Experimental Station was evaluated and the titer of 'Ca. L. asiaticus' was determined in trees with lowest HLB severity. The results showed that the C. reticulata genotype 2 had the lowest HLB severity value in the last evaluation at 35 months after transplanting and it did not differ from genotypes 1, 3, 6, 7 and 8 but differed statistically from genotypes 4 and 5. The ‘US-942’ rootstock showed the lowest AUDPC value. The twelve lowest AUDPC values corresponded to treatments of the genotypes 1, 2, 3, 6, 7 and 8. The genotypes of C. sinensis presented a fluctuating pattern of HLB severity over time, which remained between medium and low and did not increase from the first to the last evaluation in the genotypes ‘Rico 3-80’, ‘Rico 5-50’, ‘Helada’ and ‘Lares 82’. Likewise, the 'Ca. L. asiaticus' titer per gram of midribs was between medium and low with 107 and 108 log values and the genotypes ‘Rico 7-56’ and ‘Pietri 3-34’ registered the lowest titer and they did not differ from genotypes ‘Helada’, ‘Frontón’ and ‘Rico 5-50’. The rootstock ‘US-942’ conferred effect of low HLB severity in C. reticulata experiment in which genotypes 1, 2, 3, 6, 7 and 8 showed less disease accumulation. In the agroecological conditions of the Adjuntas Agricultural Experimental Station, the C. ×sinensis genotypes show no significant progress of HLB and should be considered in future research to determine the most favorable prospects for the commercial production of sweet orange in the island under different conditions of HLB infection.