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By Simon Baskett / MADRID (Reuters) - Valentino Rossi begins his bid for a sixth successive world title at one of his happiest hunting grounds when the MotoGP season roars into action at Jerez this weekend.

The 27-year-old Italian has won six times in all classes at Jerez and a fifth win in the top category on Sunday will make him the most successful rider at the southern circuit. It would also be a good omen since Rossi has won the opening race of the season for the past five years and each time has gone on to take the title.

"I love racing in Spain and I have many fans there, so I always look forward to the race in Jerez," says the Yamaha rider.

This year could be different as the king of MotoGP will have to fight off new, young pretenders as well as two of his oldest rivals.

The young guns include 20-year-old local favourite Dani Pedrosa, last season's championship runner-up Marco Melandri and American duo Nicky Hayden and John Hopkins.

Much of the attention in Jerez will be focused on Honda's Pedrosa who will be making his debut in MotoGP after winning three successive world titles in the 125cc and 250cc categories.

The Catalan's frail exterior conceals a steely determination that matches that of Rossi, but he is anxious to play down his chances of a title bid in his first season in the top class.

"People are expecting too much from me in my first year and I'm concerned that I might disappoint them," he told sports daily Marca on Thursday.

"Everyone is saying that I'm the one who should be out there winning, but there are five or six other riders out there with three or four years more experience than me.

"I'm not the leading challenger to Rossi, there are other riders who should be taking on that role."

Although it is the younger riders who have grabbed the pre-season headlines, two veterans have not yet given up hope.

Rossi's old foes Sete Gibernau and Loris Capirossi look to have a truly competitive bike at Ducati and were the fastest riders in the final pre-season testing at Jerez, where Rossi struggled.

"I think we are well prepared for the first race," says Capirossi. "The team and Bridgestone (tyres) are really strong at the moment and my bike feels perfect for Jerez after the set-up modifications we made during the final tests."

Gibernau, second to Rossi at Jerez last year when the Italian forced his way past him on the final corner, is also upbeat about his prospects in his first season with Ducati.

"It's going to be a tough year, but we are strong mentally I'm ready to fight and give my all, and if we get the results the payback will be amazing," says the 33-year-old Spaniard.

Qualifying for the MotoGP race begins on Friday with the shoot-out for grid places taking place on Saturday.

In the 250cc class Spaniards Jorge Lorenzo and Hector Barbera will be looking for a winning start as they bid to succeed Pedrosa, while the 125cc race looks as open as ever.

((SPORT-MOTORCYCLING-SPAIN; editing by Alan Baldwin; +34 91 585
2161))